Since it has been very poorly maintained, not likely. Expensive repairs - $500 + to fix Oil leak, sharpen blades, check belts etc. Get Compression checked FIRST if going the repair route.
It seems many oil Filters are built in India. Fram does not have a good name in Filters. I believe that Companies like John Deere have certain Specifications that filters must meet. Who knows if this is ever checked or not (Micron size that passes).
Use the largest size possible Dealer...
You have it well in hand it seems. Backup for Backup. The switchover works well but the Propane adjustment should be constant with no adjustment required. Propane has Less BTU energy than Gasoline. Burn temps are within 35°F of each other in the 3,450 F range. What IS damaging is using E-15...
Are you considering using Gasoline AND Propane on the same unit? Different Carburation is involved. Propane does NOT damage Pistons. I use N.G. in my 14KW Generac. A 20 lb tank is quite small to be used on a Generator.
Do NOT engage your blades at idle. Belts are stretching.. Blades are NOT to be a knife edge but actually square, 0.050 vertical gives 2 cutting edges.
This Topic should be ended now.