5k Pentosin leak - long & detailed

[Iain Mannix]

OK, so I posted yesterday saying that my new 86 5kcsq had a
flashing brake light for no reason.

I lied.

It is _leaking_.  From the reservoir.  From the beginning -

Bought an 86 5kcsq from a friend/mechanic in Boulder to replace
my not-so-gracefully aging 87 5kcsqa.  The 87 needs valve seals,
possibly a valve job, a starter(soon), the starting problem
fixed(cranks FOREVER), rear clunks galore, clutch is
questionable, a paintjob, etc etc etc - maybe it is time for a
new car.  Found the 86 - needs interior bits(87 has those), a
headlight(87 has that), stereo, etc.  The 86 is a strong running
car, has a bit of a grind in 2nd or 3rd (but never both at the
same time, that's an interesting one, but the 87 has a tranny),
basically, all of the good stuff on the 87 could be put to use on
the 86, and the bad stuff on the 87 is largely good on the 86.
Match made in Germany?  Something like that.

I asked about the basics WRT the 86 - timing belt, hoses,
bushings, etc.  All good.  When I picked the car up Wednesday
night, it had no brake light issues.  Drove it 50ish miles,
parked it, put a throttle cable on, changed the tranny fluid to
MT90, drove it again - brake light.  Initially, nothing seemed
wrong - but through Thursday and Friday, it became apparant that
there IS a leak, contrary to my original posting.

It appears to be leaking from the cap.  I found that the car had
no plunger/level sender when I topped off the fluid - put the
plunger/spring/washer in from the 87, no change.  Tightened the
hose clamp from the brake master to the reservoir - thought that
was it.  No.  Tightened the bigger hose that comes from the pump
to the bottom of the reservoir(bottom-side, not the one directly
off the bottom that appears to go to the bomb).  That clamp was
loose, but still no change.  Cleaned the top of the reservoir
thoroughly, drove it 30ish miles this morning.  Went from the
full line to "fill me" in 15, same on the way back.

It appears to be leaking from the cap itself, based on the mist
of Pentosin on the firewall, the wetness on top of the reservoir.

The cap has a good rubber seal in it.  Currently, the spring that
normally goes between the washer and cap is out - I theorized
that the spring is pushing against the cap, causing a gap - the
car did not leak a bit before I picked it up, and it had no
spring/washer/plunger.  Ok, that's not it.  It seems as though
something is pressurizing the reservoir - I don't KNOW this, but
I was not under the impression that the reservoir should be
pressurized.  Correct?

Questions:

Is the reservoir supposed to be under pressure?

If not, what could do that?

I've never heard of a leaking reservoir - it _looks_ ok, but
maybe there's a crack at the base of the threads facing the
firewall - is this unheard of?

Any thoughts?

Where does the rack normally leak from?  I do not see any leaks
in the rack; it appears to be coming strictly from the reservoir.


Don't know.  Not what I wanted to deal with on a new-to-me car,
but oh well.  I might swap reservoirs between cars tomorrow, see
if that fixes things.  All I can think of - but if my suspicion
that the reservoir is NOT supposed to be under pressure, that
won't fix anything.

Thoughts?  Some sort of check valve in the PS/booster system that
is allowing the reservoir to be pressurized?

Thanks - I've been lucky enough to have avoided Pentosin leaks
that are not plainly obvious - had a couple of hoses go, they're
easy to figure out.  This one is weird to me; hopefully, this is
not weird and the answer is "replace the reservoir."  Is that a
possibility?  Unfortunately, I can't replace it today and find
out - wanted to get insight from the masses first; anyone ever
have a reservoir fail like this?  Is this weird?


Thanks!


Iain Mannix