Cost of fixing mirror motor gremlins

[AK74]

Our 2002 4.6is has the dreaded mirror motor gremlin! To make matters worse, the warranty period has expired, so basically I'm footing the repair bill. I know the mirror issue has been discussed multiple times, so apologies in advance for dragging it up again.

I've searched previous threads, and the symptoms seem to be an annoyingly common occurence for a supposedly high-end vehicle. In brief, it's the 'usual' problem: hit the fold button / the mirrors go in / then immediately fold out again.

I took it to my local main dealer today for a FastLane diagnosis, which confirmed what I basically knew already. I'm going to repeat the comments on the technician's service sheet, as I'd like advice/opinions on a couple of points:

Calling fault memory in diagnosing system - fault with mirror motor on offside (it's a RHD vehicle) but could possibly be both mirrors - not sure until offside replaced.

Replacing 1 mirror motor £520 inc tax (that's $1,060.08 at today's rate)

My first question is this: in other people's experience, is it likely that replacing one motor will cure the problem?

My second question: for those of you that had to replace the motor at your own expense, and taking exchange rate fluctuations into account, does the cost seem rather high to you? I'm thinking it could be cheaper to order the part(s) from overseas (the US most likely) rather than from BMW UK. I've read good things here about Morristown BMW and Crevier BMW...I'm tempted to see if the cost would be lower if I got the parts from them, even once international shipping has been factored in.

To add insult to injury, whilst I was on the way there the 'Check Brake Light' / 'Check Tail Light' warning appeared in the display. I thought it was just a bulb that was failing, thereby requiring a simple replacement. I was a little irked to learn the diagnosis revealed that - and I quote from the service sheet once more - new o/s/r light unit required as all contacts corroded (cost £185 / $377). Has anyone else had this corroded contacts problem?

Thanks

Alex