I made the shafts on my mtx75 at work on a lathe and milling machine , did a clutch on a w reg fiesta last night, it has an ib5, looks quite similar to the bc box, and it had the distinctive whine in 1st gear lol! its only done 63k miles. You must have to change the diff bearings if you put an RST LSD into an ib5 then? the casings are def more webbed and look stronger, but its the 1st motion shaft bearing that was always the prob IMO.