Hopefully this will help others....
I have been suffering from major gear-lever rattle for ages on my 4 and had been searching on the forum for some pointers. There was lots of info about the anti-rattle spring and the fun of getting it back in place without popping out again, I found this helpful and was able to replace this without any probs.
My issue was that the rattle still persisted, reinserting the spring/plunger, then replacing the spring/plunger didn’t make any difference at all whenever I chatted about this to others I was given rather gloomy news of possible impending expensive gearbox failure.
I then came across some references to adding some rubber sleeving over the bottom part of the lever hidden under the spring retainer. This seemed worth trying, so I used some 5/8” internal diameter heater hose and cut it to fit really snuggly under the spring retainer (fitting the spring over it first, then sliding the two pieces over the lever worked best).
This did help - I had almost no rattle when in top - unfortunately still bad in the other gears.
I was chatting to my dad about this and he mentioned many years ago that a well-practiced way of improving this on some old MG’s he’d owned was to wrap the entire lever with a bicycle inner-tube - after we stopped laughing he did say that you couldn’t see it under the gaiter so it wasn’t much of an issue.
The more I thought about it, the gear-lever wrapping - as well a acting as a sound damper - would also stop the lever itself contacting any other metallic bits to cause metallic noises. So I started re-thinking the tubing idea and wondered if I had misunderstood the descriptions - or maybe they were just a bit cryptic - and there were never any pictures.... so I thought I’d try a different approach.
this time I wanted to make sure that the tubing extended through the spring-retainer so that it had a chance of damping anything from underneath and cushion movement between the lever and the retainer itself. I chose to try some thin-wall tubing which, as luck would have it, happily sits inside the hole in the retainer when fitted on the lever.
After fitting this, the good news is that I have a lovely rattle-free lever in all gears
The tubing I used was clear, had internal diameter of 16mm and outer diameter 19mm, cost a couple of quid from eBay and slides over the gear-lever easily with the addition of a bit of rubber-grease.
I have attached a couple of pictures for others who may find it helpful.