10hp compression - what is good? General questions

According to her the mower started to miss then over the course of time (as it got hot) it gradually lost power. I started it up - it was definately missing but had really good power. I checked the points and they appeared good. Instead of messing with it I brought it to a good shade tree mechanic and let him tear into it. His immediate "guess" was that a valve wasn't seating correctly or was burned. He checked the compression and it was at 105 PSI - I thought that was good be he felt it was a little low. After checking the timing (OK) he pulled the head and found the exhaust exhaust valve wasn't seating correctly. I stopped by later and he showed how the edge of the exhaust valve was not shiny which he said indicate the valve was not making contact with the seat (the intake valve was shiny on the outer edge). He plans on grinding the valve(s) and putting it back togather.

Questions - does what he described indicate the valve was not seating? What is the proper compression for Koehler 10hp? He said the exhaust valve might need to be replaced - said the stems stretch if they get too hot - is that common?

I trust the guy's honesty but I just want to varify his abilities (or better inform myself on what he described).

All told he says it will cost about $110-$130 dollars if he doesn't need to buy a new valve - and that includes cleaning the carb. He did warn that on an old engine like this when he gets it running at its proper power level it might start burning oil (burns no oil now).

a compression tester doesn't tell you much on these engines. A far more accurate way to determine the trouble with your engine is with a cylinder leakdown tester. You can buy one from Harbor Freight for less than $50 that works great on these little engines. If you don't have one, you'll need a small air compressor as well. But that will come in handy for a lot of other tasks, so is a good investment.

It'll tell you if the valves are sealing properly, or leaking, and which one. Also, will tell you if the rings are badly worn. Basically, it pressurizes the engine with compressed air, the guages tell you how much air pressure is going in the cylinder, and how much is leaking out ( won't hold the pressure going in). By listening, and feeling around the carb, muffler, and dipstick, you can find the source of where the air is leaking out. no engine is 100% air tight though. Even a new engine has some air leaking by the rings. You should get very little past the valves though.

Also, the Service manual for these engines is available from Kohler's website for free. its about 15MB, so a high speed internet connection is recommended for that. But dial-up will do it, just may take most of the night.