I wouldn't try to judge the gas that's in there now; even if it's not totally varnish, the octane will have degraded severely, and I'd expect it to be at least partly congealed, so I'd take option 1 above off the table. The least I'd consider is draining as much as possible, adding good gas with a fuel system/injector cleaner and water absorber added as well, changing fuel filters, and running the tank through as fast as possible, doing a few cycles of this with repeated fuel filter changes. You might choose to add only 5 gal. or so the first time in case it doesn't work and you have to drain. Downside risk is that there's enough gum in there to give you trouble even with those measures, and the safest is obviously option 3.

__________________
Craig Bethune

'97 SL500, 40th anniversary edition

'04 Olds Bravada (SWMBO's)
'06 Lexus ES330
'89 560SL (sold)


SL--Anything else is just a Mercedes.
(Kudos to whoever said it first)