Since this is the finest collective brain trust I know, I am hoping you can help me with this canner. Presto 7-B, looks old but in good shape. I want to learn how to can, is this worth holding on to? Or are there better options?

The rubber rings can get bad. they are sold on line. most county ag offices will check the gauge for you at no charge. if you want to can its worth hanging onto

There's really nothing to go wrong with canners, short of corrosion or physical damage, other than the rubber seals which are meant to be replaced on a regular basis. That and having the pressure gauge checked every so often.
As long as the seals are available and in stock you should be good to go.

I use one that I think is 60+ years old. Have replaced gaskets. Have seen one warp before.