Ok first off you have a bad wire somewhere, probably near or at the taillights. Your brake light power wire is going straight to ground somehow causing the fuse to blow. Putting a higher amp fuse will not fix the problem. It will only put more stress on the wire, causing it to heat up and melt down. Check your taillight bulb sockets for corrosion or bad wiring.
Synthetic oil is good but more than likely you will create or worsen current oil leaks. Synthetic is good for a new rebuild after break-in has been done. If you're hell bent on synthetic's, try a synthetic blend first and see if the leaks stay at bay and then switch to full synthetic if you still want. This is just my opinion, though. I run synthetic in everything i own top to bottom. Reason I do it is because I have seen the advantage first hand with my dad's trucking company.