I'd change the rear main, also change the input seal, bearing guide and bolts, upper and lower fork bushes and both shaft side seals, use a genuine rear main seal too. Any garage can do it, preferably the one using the correct tool for placing the rear main in, or at least a respectable method! (BMW 2 year warranty invalid if they fit it wrong) These leak reasonably often so it's worth having the peace of mind of a two year guarantee at any BMW centre in the U.K. for parts and labour. You won't get it anywhere else, but the catch is you have to authorise stripping and they have to accept it was fitted correctly. Anyway, that's what I did. The reason for changing the guide and bushes is for the benefit of the lightest pedal, the bushes go brittle and gum up, with little value in cleaning. The guide can form a step hindering bearing movement.
Fit an LUK clutch kit, flywheel if required, you won't know until checked for play/condition. LUK only make clutches, and are in this case, the OE supplier to BMW except the release bearing, if you want OE here, go buy one to use with the LUK kit and ebay the LUK one maybe. Both are ok, but the OE is SKF, the LUK is something else.
All garages will take a short cut they think will help them beat the book time, you can't avoid this, but you can discuss it, but my point is there is a risk things don't go back quite how they should always.
Only my 2p. Don't leave a heavy clutch, so many do, often not noticing from daily use that it is getting stiff, and will be unaware of consequential damage that can occur over time. Sorry if more info than required.