Engine rebuild for a 1977 30D

I recently came in the possession of a 1977 300D. The car seems to run great once I get it started. I took it to a local Benz mechanic who adjusted the valves and ran a compression check on it. He told me that
three of the cylinders were running at about 340 to 350 while #3 and #5 were running at about 230 and 240 and recommended an engine rebuild at a cost of about $6300. Kind of pricey for a car that only cost me $300.00. My question is since the piston rods seem straight and everything else looks OK, could I pass on a rebuild at this time and just change the valve seals?
Thanks in advance.
P.S. If anybody knows where I can get a copy of the vacuum schematics for this car it will be an early Christmas present.
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If you really want to know if the compression loss is through the rings or through the valves, have someone do a complete leak down test to see exactly where the compression is going. Valve seals would not cause a loss in compression, but bad valves/seats would. A valve job or remanufactured head is cheaper than a whole motor.
Scott D

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seals?
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Scott is quite right to suggest a "leak down" compression test to determine if the valves or the piston rings are causing the low compression in #3 & #5. A rebuilt head could solve the problem if the valves are implicated.
You don't say how many miles this car has traveled, IMHO 250K miles is about the expected useful life of this engine given normal, not excellent, maintenance.
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I am not sure how many miles are on the vehicle. The odometer does not work and it is not original anyway.

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Maybe now you know why you got the car so cheap! But let me add to the above suggestions: to only do a valve job will only gain you some temporary benefit-- the increased compression and heat on the old rings will cause them to go out quickly (assuming they aren't weak already). If you really like this car find yourself a good used engine to install.
--Geoff '84 300D
Cris Radaneata wrote:

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