Might swap radiator caps to check your theory. FWIW, a late 80's Honda Civic rad cap is the same as many OE moto rad caps. Considerably cheaper, too.
My experience with head gaskets (and radiators, for that matter,) is that there is no substitute for just fixing the problem from the get-go. I'd stay away from the magic elixir. Although it might temporarily solve a gasket issue, the damage it can inflict on other moving parts can be catastrophic. Your $20 goop ends up costing you $1000.

 

Get your mechanic involved before resorting to the elixars. my opinion to that.