Are you talking about the knuckle-joint that connects the steering column to the rack? They can be reconditioned with new pins, but they can be bought as new old stock from a nissan dealer. I think it might be worth taking a trip to a scrap yard and having a look at the joint on an early non power steering model k11, to see if they are the same part, or interchangable. It's very unusual for that part to need replacing, they usually last for the life of the car.
Yes new parts can still be bought for the k10, i buy new part quite regularly from my local dealer. You're best going to scrap yards that let you walk around and remove the parts yourself, so that you can look at things yourself. I think the mot man either meant the constant velocity joint (cv joint) or he was just trying to get money out of you.
The only known issue with the k10 steering rack is that when the mounting rubbers become badly worn, they allow the rack to slide around in the brackets when you turn the wheels. I had that problem with my super s but that was solved quickly, i just bought a pair of new rubbers from the dealers, for i think about £10ish each.
The best advice i can give you at this point, is to ask somebody to sit inside the car and just turn the steering wheel slightly back and forth in each direction. While they're doing that get under the bonnet and watch the steering rack, see if it slides around in it's mounting brackets. If it doesn't then watch the knuckle-joint to see if it has excessive play in it.
If both these things are fine then there is nothing wrong with your steering and you should take your car to another garage for mot testing. (Y)
sorry for being a grave digger, but as luck wouldn't have it: my universal joint (the lower one on the engine side of the firewall) has lots of play too. its from 1985. I originally suspected internal rack wear but after looking under the hood while doing the gentle steering wheel wiggle the culprit was found
I'm goanna take the lower steering link off/out and get it on the bench with a view to fabricating replacement parts....I'll post more info-pics-progress if the project is a go-er....watch this space