I just released a video on my youtube channel that talks about replacing the coolant reservoir in a 1994 XJ12 but this same procedure applies to a 1990 - 1994 XJ6
https://www.youtube.com/watch?v=bLTgw8ZwcUg - Replacing coolant tank 1994 XJ12
If you find the video interesting or useful please give it a like and subscribe to the channel.
When my helper leaned heavily on the tank when we were doing some other work, the two plastic pipes that supply/return coolant to the header tank snapped off.
I had a spare tank in my parts stash but instead decided to try and repair the broken one. I dug out a length of steel brake line and cut a couple of 3" lengths, heated them up red hot and shoved them into the tank where the plastic tits used to live. Ran a drillbit through to make sure hot plastic hadn’t blocked the new “pipes” and fastened the hoses with a pair of hose clamps on each. Looks like nothing ever happened and works just fine.
I also have a spare tank that one of the small nipples broken off. I might try this with that tank.