I have about 50 gallons in my tank that's been sitting for about two years. It looks pretty good, but not sure if I can use it. It doesn't have any varnishing, water, or sediment in the tank.

If the drum has been opened its done, theres a ratio of octane loss per time of exposure to outside air even if its re-sealed,, dont know the exact numbers but its substantial

Race fuel does not deteriorate like gasoline. I would use it.

AV gas doesnt, race gas does, its your engine IMHO!!!

Looking at Pantera's website a 28' Pantera holds 140 gallons. If this is true then I have about 100 gallons of this crap.

Take a sample and try to ignite it.

It'll still ignite, but the octane rating has gone WAY down, Ive got a dead motor to prove it

Can I add new race fuel or 93 and octane booster and run it???

Its still an unknown unless you have a way of testing it,,I think you have some expensive lawnmower fuel on your hands!

I am not that familier with race gas, but if its unleaded, then just mix it in small quantities into your car or truck. Your looking at $150 to $300 worth of fuel. If its leaded, then run it in small quantities in your motorcycle, or perhaps straight in your lawn mower.