GTV6 Master Cyl. Rebuild Consternation (long)

["Herbert Neily" <neily@domain.elided>]

    Last weekend, I learned how a blown brake master cylinder seal can
result in a dense smoke cloud emanating from the exhaust pipe.  Having been
dealt a host of financial setbacks in the last month, I decided that I'd
economize by rebuilding the MC instead of buying a new one [cue the ominous
music].  So, it was off to the trusty International Auto Parts catalog for
the requisite kit.
    The catalog stressed the need to know the manufacturer of the master
cylinder before ordering a rebuild kit.  I couldn't find any indication of
manufacturer on my master cylinder.  I disassembled my master cylinder and
measured the pistons at exactly 22mm.  Under IAP's "Alfetta, GTV6, Milano"
heading, there were kits for two manufacturers' MCs - the Item 4822 for Ate
and the Item 1409663 for Benditalia.  Since my car isn't an Alfetta, I
ordered the Item 4822 kit for the Ate MC.  My existing MC pistons looked
pristine, so I didn't order a kit "with piston".
    This afternoon, rebuild kit in hand, I set out to do the rebuild.  I
have two problems:
    First:  The existing front (with respect to the front of the car) MC
piston has two distinctly different rubber cup seals on it.  Unfortunately,
the Item 4822 kit (FTE Automotive GmbH "Dana" #RK22244) contains four
*identical* rubber cup seals (which seem to match the cup seal at the other
end of the front piston).  Therefore, I can't replace one of the existing
front piston seals.
    Second:  The rear MC piston is part of an assembly comprised on the
piston, a brass rod surrounded by a spring, and a brass hat on the end of
the rod (the hat retains the spring on the rod).   It appears impossible to
remove the single rubber cup seal from the rear piston without removing the
spring and its retaining hat.  I can't figure out how to remove the
retaining hat.  Viewed from the end, there appears to be a slotted screw
"inside" the hat.  However, no amount of torque seems able to budge the
screw (there's no sign of any corrosion anywhere) and I'm beginning to
wonder if I'm looking at a screw head slot at all - maybe it's a slot-like
peen that *permanently* fixes the hat to the rod?  Is this why IAP offers a
kit "with piston"?  If so, I'd be nuts to spend $66 on the "with piston" kit
when I can buy a complete new MC for $82.
    I'm further puzzled by the fact that the Item 4822 kit contains the
*four* aforementioned cup seals, when my MC contains a total of *three* cup
seals.  I suppose it's possible that a previous owner replaced a failed MC
with a take-off from an Alfetta, though it seems unlikely.  Even if I do
have a Benditalia MC, I'd still have the problem with the (apparently)
non-removable spring retaining hat on the rear piston.
    I've emailed IAP's technical department with essentially the same
message, but I thought that another digester might be able to offer some
insight.  Thanks.
Bert Neily
Raleigh, NC
'84 GTV6
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