Repair or replace depends on where it is leaking. Valves and other attachments can be replaced if they are leaking. If it’s the tank itself definitely replace it. Best to go to one of the bigger propane dealers who should be able to inspect it and make a recommendation. 

Thank you Scott iv , Extech, and Fred Heath! I am bringing her into the shop today to get a new cap and rotor put on and I will ask about the timing (though I imagine that was set when he replaced the timing chain and guides) and also about checking for excessive exhaust back pressure. I may also take it for a spin up the grade and see what happens with more of a challenge. 

Again, thanks so much for taking the time to share your thoughts here. I really appreciate it. 

Couple additional considerations: condition of the fan shroud, and ensuring air is out of your cooling system (burping).