I have a Minn Kota Turbo, 40 lb. thrust trolling motor, and I think it's about 12 years old. Is it possible it can get weaker and slow down over time? I have a brand new, charged battery, that I use with another smaller boat also, so it's doesn't seem to be the battery. Thanks.

It's possible. Brushes wear, electrical contacts oxidize, causing the motor to draw more amps.

Mono can get wrapped around the prop shaft, causing binding and wiping out seals.

You bet they do.

yes, things can wear out.

If the problem is not line behind the prop, what do I do? Is it fixable?

If the problem is not line behind the prop, what do I do? Is it fixable?

It is if you have the knowledge to work through the electrical pieces involved in repairing. You will need the testing equipment to check it out also.

Try to locate a repair facility near you and go by and have it diagnosed.

Good luck

If you have a basic knowledge of electric motors, you can take it apart and try a good thorough cleaning.  I did it a while back to my TM and was shocked at the amount of built up crud inside of the engine housing.  The brushes were so loaded up with gunk, I was surprised they were able to make any contact at all.  If you go that route, be careful doing it.  The brushes can pop out very easily.  They're small, don't lose them.  That may help if it's an older motor.