Hello Dave, it seem as if you are among the group who really understands preventative maintainious.
I don't recall if I related to my "El Cheapo" method of transmission service?
I'm a top sider and have been since the Benz was new. I change the engine oil between 3500-5000 miles. The engine oil level is down 1 1/2 qts. at change time. Fresh oil really saves those valve stem seals and giudes.
At the same time I suck the transmission sump dry then top it off with 3qts of transmission fluid. So the old tranny gets a fresh drink of fluid.
The oil pan was removed at 35000 miles by the dealer and has never been removed since then.
It is approaching 200,000 now and still strong.
I might add that I change the power steering tanks fluid the same way at the same time.
The differential lube with Lubri-moly is changed annually.
Using my homebuilt pressure brake bleeder, I change the brake fluid annually too.
My 1987 300E is an example of the performance you recieve by taking care of your toy.
Keep up the method you are doing and you too can have a 200,000 mile gas engine performance.
Happy Trails Beep Beep from the Spiderman in Houston!!!