Vire 7

I own a bayfield with the Vire engine and am looking to exchange information with Vire7 owners where-ever I can find them.  My Vire 7 runs reasonably well although I think I should pull it out and redo the gasket between the crankcase and gearbox as it leaks a little.  I was particularly interested in the cloudy yellow color of the gearbox oil.  As my engine is modified to a pully driven water pump I no longer have to concern myself with water intrusion to the gearbox. That being said what could cause the gearbox oil to look like that? Is it a normal condition resulting from viscosity breakdown?  I do not know if it is something I should be worried about.  I use zinc pencils inserted through a rubber bung in place of the zinc frost plugs,  works great and replacing is a 2 minute job that I do about every three or four months.