The OS engine is probably junk. The cost of replacement parts will be virtually as much as the price of a new motor. In the case of the TT, I suspect that you are leaving the engine for prolonged periods with fuel in the crankcase. Since you live in a area that suffers from high atmospheric humidity, the alcohol in the fuel absorbs water from the air, which is what is rusting your motor. If you use high nitro content fuels the problem is worse. Use an after-run oil to reduce thge liklihood of internal rusting. Automatic transmission fluid works very well as an after-run oil.