Brake reservoir sight glass replacement?

Can it be done?? It seems a lot of the professional places that offer rebuild services replace the glass, but I cant find the part anywhere. Any help guys?

If you use google you will find replacement sight glasses. 18mm is the common size. There are youtube videos too.

I used watch glass to replace a reservoir for a Honda Interceptor. It had to be glued in. Worked fine...
Get the measurement and hit up eBay.

I investigated a replacement sight glass as a just in case some time well over a year ago.
The following is from my notes for the 81 KZ650-CSR & a KZ750-H Ltd.

The glass disk is encased in a metal ring & there is a gasket around the ring and the sight glass assy is press-fit into place.
The gasket has a deep groove that the metal ring fits completely into, so the metal ring is kind of encased by the gasket/seal.
Using a HarborFreight digital caliper: (the measurements are kind of approx as I was getting different numbers measuring several times).
24.8mm gasket OD. 23.3mm gasket ID. 23.00mm metal ring OD. 19.1mm metal ring ID.
gasket w ring = 25mm OD & 18.5mm ID. metal ring = 23mm OD & 19mm ID. 6.75mm deep.
m/c orifice = 24.8mm ID & 7mm deep (since there isn't an o-ring, this orifice does not have a groove).
For replacement glass: glass button. 2mm / 2.5mm mineral glass

Z1Ent has an oil gauge sight glass that may fit, but I've never heard of anyone using it on a master cylinder. Kaw & Suzuki. 25mm should be correct, but I don't know how deep it is.