If it ain't broke don't fix it. Seriously, I believe most of the 300E's never have to have a timing chain IF the oil has been changed regularly, and the water pumps usually give warning by leaking a little before really going completely out. So just watch for coolant leaks where you park and keep a listen for unusal sounds on starting and idling. This motor should be real quiet and smooth at idle assuming motor mounts are good and engine is tuned correctly.

Mine has 185,000 and I just recently had to replace the serpentine belt and the water pump. There has been no signs that I should be concerned with the timing chain, but I did have to replace a rubber bushing in the belt tensioner shock absorber. Now everything is back to QUIET again.

Just enjoy driving your car, and change the antifreeze every 2 years(MB brand) ... that will help the water pump to last a little longer than it might if antifreeze is not changed.

Luck to you,
DanielW