[ Crossposted with BenzWorld]

I have had my ML 320 from new back in June 1999, and it has just topped 98,000 miles. For the last two years or so I have been adding oil between services, increasing to 1qt every 1500 miles by my reckoning. I learned early both from MB paperwork sent to me and from this list that some engines qualified under the class action oil sludging warranty (150k Miles/10 Years) caused by the FSS change from organic to synthetic oil in the early years. The threshold of oil usage to trigger the warranty I heard first was 1L/1000Km, and later 1qt/1000 Miles, both lower than my usage calculations.

A recent pool of green fluid under the engine, which at first I thought might be coolant, had me book a service visit. The fluid was actually oil from the AC compressor system which had been dyed for a previous leak test. The compressor was cracked and AC components needed to be replaced and recharged. I do drive on unmade roads.

At 98k Miles I was also due to have the vehicle in for service to change the spark plugs, transmission fluid, and perform a thorough check for any other issues, as well as an A service. I understand from the many DIY posts on this list that these maintenance operations can be done by those with the skills, tools, time, and confidence in their work, but as I am not a mechanic and this vehicle is often driven by family members I prefer to pay the dealer prices to have the job done by professionals and have them responsible. 

My service advisor gives me great confidence. He recently had MBUSA contribute 50% of the rust repairs on both vehicles[see this post]
He quoted the AC rebuild at $1300 less a 10% discount on parts and service they have as a promotion. Coupled with ~$430 for spark plugs and ~$270 for the transmission, plus the $150 A service would be a healthy sized bill. 

I can't explain why I love this vehicle so much but for 10 years I have not had any major repairs to pay for. Thank goodness I purchased the 100K Mile/8 Year extended warranty at a 20% discount in the first year (See below, I am sure MB didn't make any money on my ML). But I am very satisfied in how the vehicle runs.

Next the SA calls and says to keep the loaner for a while, they are checking with the regional MB rep to see if the oil consumption of 1qt/1112 Miles would be covered under warranty, as the 150k/10 year Oil Sludging Warranty is almost up. Two days later I hear back yes, they will rebuild the engine at no charge. This will also reduce the cost of the spark plug install as there is less labor since the engine is being worked on.

A picture of the engine bay is attached.
I missed taking a picture of the outside, but the ground clearance was huge!

My SA called regularly and after 5 days said the vehicle was going out for a drive of 100 miles or so to reset the engine parameters and check it over. The next day the vehicle was ready, and the SA says the A service was not charged because the oil gets changed twice during the engine rebuild. They topped up the fluids etc. anyway, and found no extra items needing work. 

He also commented that the engine rebuild would have cost $5662 

Here are the details from the work order:
Client added vehicle is using oil (!)
Engine oil sludging
Check vehicle for oil consumption, check for external leaks.
None found, preformed quick test, printed out all material.
Found heavy thick sludging in oil filler neck housing
performed DTB T-B-18.00/21 Removed engine check cylinder walls OK
R/R pistons, re-ring pistons and reassembled engine and test drove OK
Parts included were piston rings, various seals, gaskets, and parts 112-016-04-20 and 112-016-03-20 for the Cylinder Head.

The final cost was ~$1860 including tax which I was happy to pay as the vehicle is in great shape mechanically and the body looks good. 

I would have to think hard about keeping it at $1850+$5662, and would probably have continued to drive it and pay for the oil until some other factor killed it off for me.

Overall I have had a long trail of replaced parts:
machine-gun door locks, 
turn signal switch, 
E-box fan, 
entire sun roof, 
gear shift bushings, 
sunshade, 
fuel sender, filter and lines, 
MAF, 
catalytic converter, 
Bose radio (fuse blowing regularly, wiring checked OK)
both rear shock assemblies, 
both horns, 
harmonic balancer, 
front ball points, 
oil level sensor, 
power steering hose/clamps

Almost everything significant and non maintenance (battery, tires, brake pads, rotors) was covered under the 8 year extended warranty. 

I use Michelin tires and found the XC-LT4 P255/70/S16 better than the Cross Terrains which wear much faster on both my MLs than the 60,000 lifetime would promise. Both tires have very good grip in rain/snow.

For brake pads I have found Wagner Thermoquiet to work best for me: low dust, quiet, good stopping, My dealer installs the pads I supply. 
Don't use them on the ML500 as the caliper difference causes terrible brake squeal.

My total maintenance and repair cost over the 10 years since new, including the most recent AC repair, is ~$10,000, including tires, brakes, scheduled maintenance. occasional paint repair, and rust repair.

I can say that I have seen my service advisor more often than I would like - he has been there since before my purchase, but he and my dealership have been great. I would prefer MB loaners but they have a fleet of Toyota Camrys all under a year old and provided at no charge when I drop off the vehicle for any reason. The ML is always washed before I pick it up, even just for an annual inspection sticker.

I still love to drive this vehicle, it has only left me stranded once when I needed a jump start after leaving the lights on, and which finally killed the 9 year old battery. I plan to keep it for another year or two.

My main point for this long message is to alert 1999 ML owners to get their oil consumption checked before they edge out of the 10 year oil sludge warranty. Plus to give some repair history info to the many newer owners of older vehicles that are posting these days - good luck! 

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