I'm new here, but I've dealt with lift cylinders of many varieties. My 99 763G started leaking externally without any loss of function, it was just messy. My cylinders had the Servon type piston seal. One thing you should know about them is that you have to warm them up before you install them. I usually boiled water on a camp stove and soaked the rings in that. Trying to do it cold will deform the seal and in some cases they break. Please use a suitable safety prop while doing the repair. I was witness to the demise of someone who used a 2x4. It wasn't pretty.
My last reseal was done with the aid of a 8x8 fence post which was anchored by concrete. You only need enough elevation to remove the rod pin and remove the lines. 5/8" heater hose can be clamped over the -6 fittings with the ends in a suitable receptacle. The fun part is putting the Poly-Pac seal in the gland. The lips of the seal face the piston.
Good luck with the issue.
I should ask if you've checked the pressure at the barrel end hose. One other possibility is the manual lowering valve not seating properly.
I'd check those two before I started in on cylinders.
By the way, does your F model have the BICS system?
