Thinking thermal overload here too. Being cheap by nature, and having more time than money (retired), I'd be tempted to get a drop or 2 of oil on those bearings if the motor seems stiff, especially if it's spent a lot of it's time sitting unused?
Worst case, you're going to have to pull the motor anyway to replace it. If access to the bearings make it difficult or impossible to oil, why not pull the motor, put a couple drops of motor oil (whatever weight oil you have handy) on each end of the motor where the shaft exits, and try it? This isn't just a patch. Many motors will go for years once this is has been done. I've had success after success with the move. If you're doing your own work it's worth a try. If you're paying somebody, maybe not so much....
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake