About a year ago I chased up everything I could find out about the 4 speed box clutch release bearings given that supply was short of NOS bearings and the new no name bearings were of doubtful quality and no big name brand manufacturer was making them. The Lotus 5 speed bearings were different with a round nose rather than flat and used a different carrier and pressure plate without the bearing platen and are still available. Another alternative is to convert to the 5 Speed setup of pressure plate carrier and bearing.
What I found was as follows:
RHP bearing 6W 1 3/8 - white plastic sleeve - the original bearing used by Ford and Lotus in the UK. I have one NOS left
RHP bearing 6W 1 3/8 - new bearing supplied by Orinoco bearings branded "RHP" and "made in England" appears identical externally to the NOS RHP bearing
FAG bearing 508458 - brass sleeve - found one NOS on the internet. If you search hard you may find more, Nice Black oxide protected steel components to reduce corrosion. looks best quality of all I have seen
FKC bearing 6W 1 3/8 - black plastic sleeve - was an after market bearing common in Australia until recently . Good quality but FKC purchased by NSK and this size no longer made, I have a couple of NOS and Orinoco bearings in UK say they have a large number of these available at same price as the new RHP branded bearings. I have used these for over 30 years without problems
No Name brand bearing - They cannot even the name right ! - Brass sleeve -- Typically supplied by most of the usual suppliers. Made in India I believe as I found an Indian bearing company selling the same bearing. Can be Ok but can fail quickly as quality appears variable.
As a final alternative Timken bearing 1505 - similar thickness and OD and flat face but 1.5 inch ID versus 1 1 3/8 ID of original. With a suitable sleeve on the carrier or new carrier will be a suitable replacement. Made by other large name, brand manufacturers as well e.g. SKF. Cheaper than new bearings from Orinoco and when I can non longer get new bearings at acceptable cost I will go down this route
cheers
Rohan