The GC engine series is a particularly tough one due to not having a removable head. Start out by spraying solvent or carb cleaner on the valve stem and alternating with using a hand held hair dryer to heat the stem up. Sometimes you can get the varnish cleaned up enough to get it running without breaking into the block.
Next, make sure the old gas is discarded for some fresh stuff. Running the engine with old fuel is what caused the varnish build up.
The GC uses a case bond silicone sealent for the valve cover and block halves, no gasket is used at those locations. You can get case bond at most automotive stores, motorcycle shops or jet skii shop. Automotive store brands like Pep Boys will be less expensive then using a brand name like Honda Bond.
If you need to break into the block you will need to re-time the cam belt, if you have to go that route let us know when you get to it.
Nevada! The last free state!
Retired Briggs MST, Honda Top Tech.
Currently full time experienced novice fisherman.
You should've been here yesterday, the fish were really biting..