I bought a Britpart motor from Rimmer Brothers and Ive had nowt but problems with it (I was in a rush and needed one that very day). I would recommend buying a genuine LR motor, they're not cheap but once fitted you should be sorted.
Got a pattern one for mine off fleabay - not sure of the make. It fits, but it's not brilliant. If I had the cash at the time I'd have gone for a genuine one, no question.
The difference in price between a genuine and a pattern motor is huge. Enough even to make you buy a Britpart motor. Even though you know you will regret it. I did