I have a Yardman tractor (I think 1980 - it is model 14918-9) with many accessories (mower deck, plow, wheel weights, chains, leaf vacuum, cart) that started acting strange. After about 20 minutes, the tractor would idle rough and then shut down. It would start back up but idle very rough and shut down again in a minute or so. I sent it to a shop and they said compression is very low and it would not be worth fixing. I am wondering whether any of the crankcase additives I see advertised to improve compression would help. Does anyone have any experience using these additives and are they good for a small (16hp) Kohler engine?