I started to answer this post yesterday but though better of it. My point would have been the price. The hundreds of valve jobs we have done to single cam MB V8s have almost all been for less than $2k. We are an independent though and in a rural area so our prices are naturally less.
The reason I am writing today has to do with the reasoning behind the job. A compression test will be of NO use. Unless the valves are bent there are almost never compression problems. The problem is oil leakin down the valve guides and this occurs for two reasons. The worse is when the guides become loose in the head and oil leaks between the guide and the head. If your plugs were soaked in oil this could be the case. This problem must be addressed immediately as the bore in the head is being ruined and the valve guide will eventually fall in holding the valve open causing it to hit the piston.
The more common problem is valve guide oil seals which can be simply replaced from the top (5.5 hours labor). For anyone experienced with MB (including most dealers) an original engine with 200K needing valve guide oil seals probably won't have them last due to the wear on the guides. So, a proper recommendation is to fix the oiling problem the proper way by replacing the valve guides. This necessitates reseating the valves as the angles get slightly changed when the new guide is pressed in. This diagnosis is probably the easiest ever made on an MB. Its cut and dried. We sometimes start by making an attempt at the valve guide oil seal replacement. We do the cylinders where the sparkplugs were fouled and through experience we judge the guides with the prearanged concept that if there is a question we will take it apart.
This concept here has so much to do with mileage. I have seen valve guides drop on engines with less than 100k, these have to come apart. But, the course of repair on a valve guide reseal for a motor over 200k has to do with experience, and experience says don't waste the time with just seals.
If the car is in good shape, someone should fix it and use it. Find an independent shop with MB experience that does engine work. Anyone with experience can do good work here as the pieces are built so well.
Bosch Master, ASE Master, L1
33 years MB technician