I need to redo our door after 6 years. It was done with an oil based spar varnish from Woodworker's supply. Does this stuff apply over oil based or do I have to strip the door first. I just finished a bookcase and used oil based varnish but it is getting harder to find.

: J. E. Moser makes a water-based spar varnish I've used on an Alaskan Recovery
: kayak frame... easy to spray, quick build-up of coats, and slightly
: ambered to look like a traditional spar. I also used it on an exterior
: door to our house as a more rigourous test... so far, so good. No signs of
: chipping or peeling after 12+ months. Of course, convenience comes at a
: price: $63 a gallon through Woodworker's Supply. It's called MarineShield.