As above, replaced the oil in my manual box last night. It’s like a new gearbox! Car’s done 117k miles. Sealed for life? What a load of rubbish! The stuff that came out was like thick black sludge with squidgy crusty black bits of sh1te in it. I filled it with castrol ATF. Took me about 45mins in total, but I was taking my time. All you need other than basic tools is a pump to put the new stuff in there, and a torque wrench if you wanna torque the plugs back up properly. I got a “syringe type” 500cc pump for about £15 from a tools wholesaler.
I’d strongly recommend this to anyone with over 100k miles. The difference is absolutely unbelievable. I honestly can’t believe the difference it’s made, I was only changing it as a matter of course, and for a bit of fun coz I like to mess. It's so smooth now, actually feels like a different gearbox. I’ll be doing the diff very soon, coz if the oil in it looks anything like the crap that came out of the box then I want it out of there asap!
By the way, to anyone thinking of doing this, gear oil smells awful, be sure to wear overalls and have plenty of rags ready.