Try "captain Tolleys penetrating sealant". Its real and works.

 

Great, thanks Pistol P. Will it cause issues/more work when I get the screen replaced & rust sorted?
Was going to use tiger seal or similar but concerned it’d be a ******* to get off when the body shop could to do the repair.

Also - any idea how to get the A post trim off? I’ve taken off all the screws I can see but the thing doesn’t want to budge. Figured I’d try to locate the leak.

Thanks

 

I seem to remember the trim comes off by pulling it backwards (once all screws out). The front-most end of it (hidden between the edge of the dash and the bodywork) has a kind of fork that slots onto a peg at its front-most point (sorry, it's difficult to explain...)

 

Are there any temporary repairs

There are rust treatment compounds that come in spray can form, creates a coating over rust, maybe as a temporary solution something like that could be sprayed under the windscreen rubber to create a seal and at the same time possibly prevent any further rust from forming.