SMCK

Aka rear pinion seal.

Had the car in for a major service last winter, drove it for a few months and then parked it for a few months due to work.
Came back to find it'd been drooling differential fluid all over so I took it to a warm garage and poked around a bit.
The differential is leaking a bit from the drain plug and there also appears to be a pretty big leak where the drive shaft connects to the diff.
I had the dealer source that seal for me but I've never done this job before so I was hoping someone else had some experience with it.
Anything in particular I should be wary of here, and do I need any special tools?

Also I checked the differential fluid level and curiously, despite the fact that it'd been sitting around dripping for months, fluid gushed out of the fill plug when I undid the bolt. The car was level. I'm guessing this is what made it bleed.

WindyCity1

I am a pretty hard-core Do It Yourself'er, having rebuilt entire cars and even a Laycock de Normanville overdrive before. When it comes to rear pinion seals - that's a job I always farm out. I'm lucky that I have a good axle shop nearby, and I know there are ways to make sure you get the preload on the bearings right - but that's not something I want to gamble on.
From your situation, I might try cleaning the vent on diff, refilling it with fluid, cleaning all the old traces of oil, and see what happens.

SMCK

Bah, that's definitely not very reassuring hehe. The seal's already shot and it's leaking too much at this point for me to want to drive it around so it really does need to be replaced.
Checking the vent's on the agenda, but I kind of feel like if there were indeed a pressure problem due to clogging they'd have noticed that during the service when they undid the drain plug and informed me to prevent damage.