Ignoramus31353 fired this volley in
:

I sold a customer this hoist, and, unfortunately, upon delivery the
sight glass was broken.

Here are some pictures:

http://igor.chudov.com/tmp/Sight-Glass/

He says that it is a round glass with a little groove for a o-ring.

My question is, where can I buy him a replacement glass, any idea?
McMaster seems to have complete assemblies only?

Ig, it's just a sight glass! If it isn't pressurized, you could make one
yourself from darned-near any transparent material that would take the
heat of the fluid.

If you can't get one anywhere else, I'm betting the optics department of
Fischer Scientific will have exactly what you want.

Lloyd