My guess is: the valves.
Let's suppose the valves were adjusted 15k BEFORE you got the car .... and you drove it another 20k or so. 35k is a LONG time for not being adjusted.
It isn't hard to do, but it is something that you either need to learn or be shown. Their are several repair books that show you. Best to use two specific 14mm wrenches made for the job.
Can you get it to a shop and have them adjust the valves?
'03 E320 Wagon-Sold
'95 E320 Wagon-Went to Ex
'93 190E 2.6-Wrecked
'91 300E-Went to Ex
'65 911 Coupe (#302580)