Head R&R
 

About how many hours labor does it usually take (barring any unforseen difficulties) to just R&R the heads on a M116? This isn't by any means a DIY job is it? Going along with that, how do I know whether my engine just needs a top end opposed to an entire rebuilt engine? Or is it worth JUST doing the top end and leaving the bottom? I have heard that the bottom ends of these cars are pretty stout. Any advice is appreciated.

Have you tried replacing the valve stem seals? Quick, cheap and easy and just might solve the problem.

Pulling the heads is within the DIY realm. The only special tools you absolutely need are offset socket bit for the cylinder head bolts and some way to pull the chain guide rail pins.

It's probably worth replacing the water pump and lower end of the timing chain while you have the heads off.

Sixto
91 300SE
87 300SDL
81 300SD
78 450SEL (sold)