Shipchief, I thought of some plexiglass too, but I think there would be no chance of seeing through the oil film on it.
With the sight tube I can mark the "tip of dipper mark" and watch it when running.
For a low level, I'll stop at 1/4" on the dipper when running which is maybe 1/2" stopped.
What about high oil level? How much is "Full"? Maybe one inch on the dipper when running, one and a half stopped?
Bruce