Well to be fair, I remember my first guzzi and as I was getting familiar with it, I looked at the plug for the timing hole and figured that was where the tranny oil must go.
Luckily I did rtfm, and I got the oil in the right place, but I thought at the time, I'm sure that others have made the same mistaken assumption, there's probably been a few out there, they're just being shy,lol.
I've done the Varsol flush before on my CalVin for a slipping clutch problem, worked like a charm, my best ever mcgyver fix.
I'll file docc's tip about removing the starter for next time, that sounds like a good plan.
To the OP from experience, when you're whittling your wooden plug, don't use hardwood, I couldn't get it to seal well,,, the wood that worked was a piece of real cheap softwood, so the fibres swelled as it absorbed the solvent and sealed the hole.
After I did two good rinses working the clutch, I took the bike out and abused the hell out of the clutch (fanning it many times)to get it good and hot and burn off any residue.
Good luck
Kelly