Bought a used Stihl 192T. It started and ran well, then seemed gutless in the cut. Compression was 130# after 5 pulls, but when I looked into the exhaust port I could see what looked like scoring just to the right. Can it test good but still be compromised under load? I don't want to spend an arm and leg on a new piston and cylinder, but I'm afraid that's what it's going to take. I see Farmertec parts out there--are they worth the money? Any other good choices? Thanks for any replies and help.