XJ900 Front brake master cylinder problem

Here's the issue:
I rebuilt the front brake calipers, pistons, pads, seals, etc. When the brakes were applied they felt strong and progressive. But the pistons wouldn't let go. I read that the problem was in the master cylinder reservoir. There are two holes in the bottom of the reservoir, one of which is for brake fluid to flow back into the reservoir when the front brake is released. Figuring this hole was clogged, I dismantled the front brake master cylinder/reservoir assembly. I cleaned it all thoroughly with clean DOT3 brake fluid only but looking at the Yamaha Service manual diagram, I noticed a part seems to be missing, the "Return Valve".

In the below diagram, the Return Valve seems to go on the end of the master cylinder piston.

If you look at my picture of the parts I took out of the front brake master cylinder assembly, you'll see everything is there except for the "Return valve" shown in the service manual diagram. What you see in the attached photo is EXACTLY what I took out of the assembly.
Rubber dust cover
Circlip
Master Cylinder Piston (with rubber collar)
Rubber spring cap
Spring

Maybe whoever rebuilt the front brake master cylinder the last time didn't include the "Return Valve" and that's why the brakes weren't working properly. I'd like to figure this out before I go and splurge on a front brake master cylinder rebuild kit that I don't need. Looking at various sites and catalogs, you don't get to see exactly what's in each master cylinder rebuild kit.

Thanks in advance for any help, advice, etc.

 

Re: Front brake master cylinder problem

which bit is labelled return valve? the parts you have removed seem all present and correct according to sub diagram 2 in the schematic.

 

The exact missing part was perhaps difficult to pick out, so I've re-posted the diagram with the "Return Valve" pointed out.

 

I believe what they call a return valve is actually that rubber bushing/ring seal that is already installed onto your machined aluminum plunger.

 

thats how it looks to me too

 

Thanks for clearing that up. Now comes the re-assembly with clean DOT3.