Hi, had my defender for 6-7 years now and i've noticed the rust get worse but very slowly where the side panel meets the top of the rear tub. I'm guessing it's down the steel bolts meeting the aluminium panels.

Anyways, I'm now getting a wee bit of water ingression and would like to halt it in its tracks. Am I best removing the bolt completely or would something like a rust curer/stabilizing then waterproof filler do the job?
I'm not really competent enough to go cutting chunks out of the side panel and patch it that way.

Any ideas? Thanks, as usual!

They are called tub cappings, roof and side panel removal (in one lump) will expose the fittings/rivits for removal and replace. Early models were galved, yours are not.
Common problem with non galvanised cappings.

No need to cut anything, but as above you need to lift the rear body and replace the steel capping. It's riveted on along the top of the rear tub. Time consuming, but not difficult. I suppose you should replace the bolt too.