I have a 2015 TroyBilt Super Bronco 50" deck with a Kohler KT735 engine (240 hours) I noticed a small oil leak around the left valve cover at the end of last cutting season. Parked it for the winter. Now it is blowing oil out of the muffler on the left side. Obviously, oil is getting past the rings and on top of the piston and I'm not sure what parts to replace. I'm thinking a head gasket set and rings. Any suggestions? I know that sometimes there are aftermarket parts available that are better than the factory parts. Looking for info on quality parts as well. TIA