It sounds like you're quite capable of the mechanical inspection and the idea that the shock has an internal issue certainly seems a reasonable conclusion at this point.
Wild idea number one for your drive back home.....
If you find the tire is rubbing too often due to road conditions you could -- perhaps--- fabricate a spacer from PVC pipe that might prevent compression that allows tire rubbing.
If you took a proper length of PVC and cut a full length longitudinal section from it, to allow it to just snap over the shock piston rod, it might stay in place and prevent compression to the point of tire rubbing. This technique has been used by some on the deck lid shocks to hold up the deck lid when the shocks are cold or failing. Could always add some Thai wire to make sure it does not slip back off.
Like I said, wild idea but sometimes any port in a storm is worth looking into.
Larry
Yes I know the iPhone dictation-to-text decided to use the word Thai instead of the word tie. I left it just because it looks so cute.
