I can't answer your question but I'd be interested to know how you made the sight glass and the material used.

The filler plug is on top of the head casting, under the top cover (below the belt). It’s a hex socket plug.

Is funny, I had to make a new sight glass as well, must be a common thing. I turned a disc of clear plastic (Acrylic?), and used silicone sealant to fix and seal. Been there 30, and looks 3mm thick.

Cheers Will

The oil originally specified was Shell Vitrea 69. This pre-ISO number became Vitrea 150, post-ISO standardisation. Current equivalent seems to be Shell Morina S1 (or S2) B 150, available in small quantities here:

**LINK** (no connection with the firm, and not a customer)

It's not going to be a critical choice, however, there's a large gear in the gearbox that is Tufnol, or a different, grey plastic that swells with age. So, perhaps, one should avoid lubricants stuffed with additives, or 'synthetics'. Mine piddled oil out from the gear-change lever's bore, but it's a simple O ring seal.