Yeh its a common problem, particular on the MK2 Phase 1 and lucily is a very easy fix. All you need to do is take off the handbrake gaitor, and the back section (2 screws by seat adjusters) and remove the cover. Then inside you will see a few bolts which basically brace the handbrake at either side of the handbrake base itself (4 bolts i think).
Basically tighten the bolts and you should find it will no longer wobble from side to side. Had this happen on my old clio and my mates was the same too, must be a design flaw - but lucily a very easy fix. The only time problems can occur is on the older models rusting can occur and prevent tou from tightening it sufficiently.
As for the exhaust, try and find some hotspots/holes on it and if you have the know how you can use some generic panelling to weld onto the holes. But having said that a new backbox for my MK2 Phase 1 was like £55 so you may aswell just get a new one i guess.