sorry dude I'm a tyro on these cars and have the opinion that if it aint broke, don't fix it...if its already broke then braking it again wont really matter!!
anyways be careful under the trim panel under the heater above the passenger foot well, there are relays and connections there, that can be kicked by the passenger and cause problems..........
I removed the passenger side under bonnet wiper trim the other day wanting to clean the "green" form the plastic heater duct etc, and also the box section connecting side to side, where the rain water etc drains........to check for possible water leaks into the car, as sometime the screen mists up, an indication of a water leak into the car?? that I learned form this great forum. the mot dude told me about front fire wall/scuttle corrosion, but ours is ok....was investigating about waxoiling that area as well, but have decided not to fiddle for now......
anyways the plastic duct did not want to come off, so rather than breaking it, I cleaned as best as possible and refitted. I could get my hand in there someways, but not "inside" the car..........one of the days I will peel back the carpet and look for water/rust stains in that area...........
I assume that the left plastic under bonnet duct is held on in a similar way to the multi electrical block on the r/h/side, under the wiper motor??
if you carefuly remove the passenger "trim" and have a look see, if the blower motor can be removed with everything else left in situe, that might be the way forward.....check in the manual, or parts exploded view......but I'm sure a real 306 guru will tell us.......
I'm still learning about these cars and improving ours all info gained form this brilliant forum.
I would be well and truly stuff without this place, I'm being honest and very grateful. thanks dudes