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burping master cylinder

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Does anyone know the function of the two sets of holes in the reservoir (one set of two for each piston; brake and clutch)? There's a larger hole that I assume refills the bore but it seems it ends up behind the main seal (towards the front of the MC, away from the outlet lines). Then there's a smaller hole that must lead into the bore too somehow? it doesn't go straight through though. I have it soaking in lacquer thinner at the moment. Here's a picture I took earlier this year when I first opened it up. Ugh. It's been run with all holes exposed, clean and rebuilt but I didn't take an "after" picture so can't show the holes in question.
dirtymc.JPG
 
I think, just by watching the piston through the hole, that the larger hole fills the bore behind the main seal, the smaller one (covered in goo in photo) takes an indirect route to refill the bore in front of the main? (the business side). I'm pretty sure I'll be fine with new seals again but I like to know how things work. Or does it all fill through the big hole and little one is some sort of equalizer passage?

Got some seals. I think it's a seal issue as the ones I got are a lot "shallower" than the ones that were in it or the ones that came in the kit. I was running one of these "skinnier" seals on the brake side because I ruined one of the ones in the kit. These "off-the-shelf" ones don't have as much of a "skirt".
PS I'm told the little hole is to let fluid back into the reservoir when the pedal is released.
mc-seals.JPG
 
Finally got another rebuild kit (from Moss, same as VB as far as I can tell). Must have been the "off shelf" seals just weren't covering that little hole quickly enough, now with proper seals, there's no burb (on the bench pushing by hand).
BTW is this thing worth it? Trying to convince someone to help me bleed will be even harder now that it's cold in the garage!
 
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