I survey, transport and repair common issues with W126 and W116 and carry a crash kit for common repairs.

Adding to the above posts: I make 1" X 1/2" x (questimate) 18.5" long to the
bottom of a knotch, sticks just incase the white nylon window slider fails. This way I can hold the window up and lock the car! I will measure them as soon as I replace several regulators.

If there is any crud on the positive battery terminal: Note a large battery can be fun to lift from this dark hole from @!X!!
1. brass terminals will be coraded past wire bursh fix. Use a Lesile battery terminal reamer or similar device and expect to remove a lot of brass. Some have taked 15 minutes per terminal!
2. wash everything under the hood. Battery acid and crud has a hunger for steel and aluminun goodies.
3. clean the leaves and other crud from under the battery tray. Wash this area.

Keep a 13/16" deepwell spark plug socket and wrench in the trunk of all sunroof cars. Now if the AC fails, you can manualy open the sunroof.

Power steering filters are never changed by DIYs. Change this NOW.

If there is any sign of DIYers, drain and repace brake fluid with NON DOT3 fluid.

If fuse box has the paper listing proper fues size per circuit, verify all fuses. DIYs love to bix & match. Remove negative battery terminal and clean fuse connections. If paper list is not in the box, GET ONE NOW.

Diesels:
Don't toss out the used per-filter before looking at it's condition. Check for any sign of alga growth. If found, drain tank and clean strainer. OH WHAT FUN!

Change the filters and keep spares in the trunk.

Verify prime pimp is in working order.

Verify battery condition and size. 50% of the diesels I have survey'd / bought have had a new SMALL battery.