1. Do not use synthetic oil, it'll leak out. Old Vs's used motor oil, dino oil.
2. Gear lube, while great, will stiffen up in the cold.
3. You already have it opened, replace the seals anyways. The body seal on the cover doesn't really go bad, but its cheap. The seal in the handle will go bad, I'd replace that. You can test the quad seal to see if it still seals.
Through my own research, asking around, etc, this is the best that i found that works for me. Hydraulic fluid(you can use brake fluid) and automotive grease. You can mix the two to your liking.