I plan on keeping my 300TE for a long time, so a year ago I popped for the whole deal at 163k-valve guides, seals, lifters, re-seat valves (don't know details; done by MBZ tech), head gasket, rolled in a new timing chain, replaced water pump & most/all hoses. Plus all attendant seals. Head was sparkling clean, BTW; synthetic oil works! Too bad mine had very early guides, so they were gone. Plus it was run on Dino oil for its 1st 68k, so who knows how much synthetic might have helped.
Car now runs as-new, and shifts better perhaps because of favorable/more consistent vacuum from the engine. Get a few quotes, but this job done properly will set you back $1,500+; I think I dropped closer to $2k because I threw in a lot of new parts- my car's 14 years old, and needs to be absolutely dependable so I maintain it within an inch of its life. I think it knows