I’ll also have a 763 but a little older as it’s an F (1999) that I purchased two years ago with many issues including oil leaks and a HF pump that wasn’t connected. I did a heap of work with it on my own place and kept fixing issues as they arose like all three ram seals. Eventually I bit the bullet, removed engine/pump and fixed absolutely everything including making new mounts and changing how the HF pump is driven off the water pump end of the engine. I replaced nearly every hydraulic hose on the machine as twenty five years and 3,000 hours had seen the best of them. I presently don’t have a single leak and a high hydraulic flow that actually works well when operating my chain trench digger and post hole auger.
For $900 dollars you have nothing to loose as you could put a couple of $k into it and still be way in front, as for where it’s leaking oil is like asking how long a piece is string is.
I bought mine cheap at AU$12k two years ago, machine had been sitting out in the weather for 4 years prior with the end broken off the tilt ram that I needed to fix before I could even pick it up. I should easily be able to get over $25k for it now in it’s present condition, but she ain’t for sale.