The bushings are probably the last thing that will wear out on a .40 LA. You will likely need to replace a couple of piston/liners and connecting rods first. The cost of these parts is high enough that you'll probably just spend a few more bucks on a new engine.

These engines are not nessesarily useless for your second plane. Just choose a second plane that normally uses a .25 to .32 BB engine. Some .25 ball bearing engines weigh nearly as much as a .40 LA. A lot of seasoned flyers use OS .40 LA engines as an alternative to .25 ball bearing engines. Likewise, a .65 LA is a good alternative to a .46 BB engine.