Ethanol Free gas is not available in Canada thanks to Trudoo and his Lieberals.
The cheap fuel now has 15% (e15) ETHAOL. oK for late model vehicles but not for small gas engines.
The water in the tank comes from condensation in the fuel container and the Ethanol process.
I never totally empty the fuel container, always shut off fuel and run engines dry and drain Float Bowl for Winter. That Ethanol (now 15%) can really seize up a Needle valve. Everyone has a different...
Try using some quick Start. It seems you are over your head in this. Check that the valves are set correctly and that the Flywheel key is in place. Clean Spark plugs.
Air up the tires to equal pressure Front and Rear. Park on a Level surface and use a 2x3 or 4 and level the deck , a 1/8" lower on front. Check both sides. Mow your lawn on an angle the next time..
Check all blades for equal sharpness.
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.