I "upvote" this statement 1,000 times. Gotta be nuts getting under a car supported by something that folds (or cinder blocks). Especially a hefty vintage MB! Pretty sure those "Quickjacks" are intended, primarily, for tires/brakes, etc. NOT intended for humans lying under the car, performing extensive maintenance.
Heck, 4 jack stands and a strategically placed floor jack have a much higher weight rating than those Qjacks, anyway. I've got a small bottle jack (among many other devices) that's rated at 5 tons!
If you want a lift, get a real lift. Lots of money, gotta have the space (and height), proper concrete base and proper installation. If you live in a temperate climate, i.e. "the south" or "out west", they can even be installed outside and easily covered when not in use. Could easily write a book on this subject (probably, someone already has), many details and lots of "do's and don'ts" when it comes to lifting 4,000lb vehicles as a shadetree/backyard amateur/hobbyist mechanic (no insult to anyone intended).
DON'T GAMBLE WITH YOUR LIFE

Thanks for the advice on the quickjacks. I used to live in "earthquake country". My 240D was on jack stands, awaiting new tires, my 500SL was on my quickjack system, as I installed new shocks & springs. After the Napa quake a few years ago, guess which car was partially on the ground? Not the quickjack'ed 500SL. I'm of the "trust, then verify" ilk. The car goes up on the quickjack system, wheels come off and are promptly stuffed under the car, or a hydraulic jack or jackstands are placed if the wheels aren't off. I think it really depends on where you are, and making the right choice based on individual situations. I don't have the clearance for a proper lift, or the flat surface outside in the driveway for one out there now that we live in "the south". But, this doesn't mean I'm not taking extra precautions just because I'm using one method or another...

I think it is always best to run the weight of oil the car was designed for.

The Dreaded OIL THREAD
 

Well ;

Yes and no =

Modern oils lubricate far better and nothing is being oiled when first you start the engine so *slightly* thinner oil gets up out of the sump and lubricating much faster....

I have a 1969 Honda CM91, 90CC tiddler with 40,000 miles on it, runs very well, I use 10W14/40 fully synthetic oils in it only...

Generally, I agree - my last post was just pointing out that the "proper" oil was not available so I used a heavier one while on a roadtrip, which seemed to immediately remedy my oil leak. The car is now back on its correct oil, and the leak(s) have not come back after 1000's of miles..