I have just done exactly the same to mine, about an hour ago!
I also took the cylinder shaped bush out and put some JB metal weld around it for a tighter fit.
The results are fan-fecking-tastic!
When I table Kied mine, I did a row each side, then went and did another row over each side again to close the gap a tad more.
Leathered it with grease and it's... it's like a new gearbox
I didn't actually think my gearbox was bad at all until I did this pocket money fix.
Anyone wanting to try this, you need a 13mm spanner.
Undo the nut that secures the weight arm to the box and remove.
You should have in your hand the arm itself, the 13mm bolt and washer and the metal cylinder with bush that goes in the end of the arm.
Cable tie the square part right along the longest sides (twice on each) and then refit.
You can also do something with the bush like I did, if there is play in it, I'd recommend it. I squeezed some JB metal weld (like epoxy) in between the plastic bush and the weight arms hole.
Once it had gone off I checked it for play - nothing. I can't see how it can fall out either as it is closed off at each end. One by the bush and one by the washer.