Well I bought a 620 diesel (V/99) this week, and I too have poor parking brake efficiency, and when I prodded the bubbly bit at the end of the rear wheel arch I got a little hole...that grew a bit! Looks like I'll be having some welding done later in the year (MoT due Nov).
Things I have done on the 600 this week : drove back home to analyse it and fixed the failing rear number plate bulb. Contacts on the bulb weren't gripped properly.
All these fine old 600s are approaching twenty years old or more now. Even youngest 99 Reg ones are eighteen years old. Out of sight and mind behind the rear wheels, they usually get forgotten and rarely serviced even by most caring users. Over the miles and years they get covered in road filth and become corroded. Provided not too far gone, I have removed these calipers, part dismantled them and cleaned them thoroughly. I also fit new rear pads at the same time. They are not expensive. Then you have to "prime" the handbrake auto-adjusters. Not to be confused with the Handbrake Nut under the centre console. That merely adjusts the cable, not the Auto-adjusters.
I have described the process which I discovered by accident years ago soon after getting my first 620ti. It's somewhere if you search. In a Nutshell, after thorough cleaning of the Caliper's Pistons ~ I use brake fluid for this paying particular attention to the seals around the pistons which can be damaged if you are heavy handed. Best to avoid that. You can get a special socket to wind the Piston back into the body of the Caliper. I wind it in fully, it will then be too slack over the new Pads. Then using the Socket slowly wind the piston out until it just slides over the new pads without being too tight. Then I bleed the calipers in the usual way. My son has just done this to his 217,000 mile 620ti using a Draper Brake Bleeding Kit which can be bought for a tenner posted off ebay. Then start the engine and pump the brake pedal to take up any slack in the pads-caliper-disc interfaces.
Sadly now retired last year, my friendly MoT tester had a poor opinion of Rover Rear Disc Brake Handbrake operation ~ years of fails did that ~ However, I think he modified his opinion after testing my own and family members' cars with comments like... "They locked out John"... How about that ...
Regular TLC is not Rocket Science for the DIYer who is unafraid to pick up a spanner. Just time consuming but, it consumes less money reducing the need to by new stuff.
This is the Socket for winding Rear Brake Caliper Pistons. :~
Eight quid posted from ebay. Money well spent if you have a lot of MGs and Rovers to deal with..
Here a close up of it used on a nicely cleaned up Piston and Seal :~
Even if they are in this sort of neglected condition ~ both were on this otherwise very tidy car :~
Fortunately, new/remanufactured calipers for most of our cars are not expensive. I even got Fifteen pounds for each old one I returned to the ebay seller. That meant the Calipers cost less than forty quid each, plus return postage which was about a fiver with Parcel2go.
Here's the remanufactured items fitted.
"They locked out John." How about that ..