Any way to access this easily? Getting at it from underneath is darn near impossible, looks as though there is an access panel on the floorboard to maybe make it easier to fix this oil leak. I inherited this car from my father-in-law upon his passing in 2020, it is an XK120 FHC with a good "daily driver" type resto on the car, otherwise great condition and runs excellent. I'm getting used to dealing with British construction/assembly methods with this car, and the oil leak at the back of the trans area is way more than just marking its spot after a long drive.
Any ideas/advice out there?

 

You can remove the gearbox cover from the inside, when you remove the carpets you can see all the screws.
Once removed you can access the gearbox.
To replace the seal the driveshaft and yoke ( One big Nut) has to be removed.
Now you can access the seal.
Good luck.

 

Got the lid off inside, was a bit of a PITA but no problem, thanks for the tips!
Drove the car around yesterday for a good 20 minutes at highway speeds and could not find any leakage! Methinks there was oil going down the shifter shafts and leaking out due to too much Lucas oil conditioner(real sticky and stringy stuff, sticks to EVERYTHING)adhering to the top of the gearbox shifter cover inside the trans and over-oiling it. Changed oil before driving it, used 1 qt. 30W oil as per Jag specs, and 8 oz. of Lucas oil conditioner(was mixing it @ 50-50 before, too much!), no leakage noted even after a 70 mph highway blast for several miles.
Will be keeping an eye on things, all things British tend to leak oil as we all know!