Front Master Cylinder Rebuild on Rear?

I'll do what I can, scotch. Cleaning it up is no problem, and while I don't have a micrometer, I do have a verier gauge. So however accurate I can get with that, I'll let you know.

EDIT: Okay, so let me know if this description works. If not, I can draw up a simple cutaway with measurements. And, as mentioned, every measurement is "best I can do with a Vernier Gauge". In any case-

The opening "lip" is 24mm in diameter, and is 2.8mm deep. The access hole then necks down to 18mm diameter, and is 13.3mm deep, measured from where the opening diameter changes. The total hole depth is 16.1mm, from outer edge to bottom. (note: this also ignores the area that needs to remain open so brake fluid can circulate correctly)

HOWEVER, the deeper, yet smaller diameter portion is not a straight-sided cylinder- the walls have a bit of a taper inwards the farther you move "into" the master cylinder. I couldn't reach all the way to the bottom with my gauge, but getting very close I got a bottom diameter measurement of 16.7mm.

Hopefully this helps.

Lucien-Harpress - once you have that area clean, could you take a couple good photos to show how that area looks? I've never felt the need or necessity to remove that plastic plug and most likely never will, so it would be good to see exactly what it is hiding.

If you can't find a frost-plug that fits, then consider this: Cut a 24 mm disc from a thin-wall plastic bottle, insert and fill the opening with epoxy.

Lucien: An automotive parts store should carry Imp. and Metric sized frost plugs.

StanG wrote: Lucien-Harpress - once you have that area clean, could you take a couple good photos to show how that area looks?

No problem. Honestly, the ONLY reason I could fathom anyone wanting to even consider it would be to get a straight shot at the relief holes to clean them if they were really gummed up. But even then you'd have to deal with re-sealing the opening, because I'm fairly certain there's no way of getting the original plastic plug out without destroying it.

As far as mine goes, I'm really liking the idea of those frost plugs. I'll look into it!

Yes it is removable.