The window on my master cylinder is breaking, I have an 04 gs500f, what years will work as replacements? and does anyone have one to sell maybe from a wrecked bike or etc.

someone on ebay was selling them.
search the forum and you might find the link another member posted.

there is a company in PA I think that sells the glas replacement for 15$. I dont remember who but Buddha knows.

If all else fails, I have a complete (nice) master cylinder for sale in the classifieds. 

I think I may have found an improvised solution to this problem by using a 16mm diameter silicone plug.

You can check it out here: https://youtu.be/gKjYFypuz2w?feature=shared

Now...if somebody wants to try this I recommend to check if the silicone plug you use will actually be brake fluid resistant. Try submerging it in brake fluid for a couple of weeks and see how it reacts.

Is the sight glass intended to be replaceable?

Is it a screw in type?

I'm planning ahead...

So I looked at my bike.

It doesn't leak, but what I suspect happened is the outer glass must have broken years ago, and all I have is a single layer inner glass left... I think (?).

In any case, I measured Φ = 17.5mm with my admittedly dodgy calipers.

Has anyone tried an 18mm sight glass replacement?

Seems like Ebay is selling 4 x  18mm sight glasses for 5 bucks, probabaly worth a try.

Thanks, I ordered some. I also ordered a rubber stopper and will pack that on the bike just in case.

However I hesitate to do anything irreversible because I don't have a leak (yet?...).

So, two questions:

1. Has anyone gotten the 18mm pressed in OK?

2. Has anyone switched to a piss jug reservoir from another bike using the existing brake line?

Thanks!

Here is a vid of a Honda mechanic replacing the sight glass on a project bike. I like how it was his first time doing this and he wasn't happy with his first attempt.

Hope it helps.