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early twin cam fours and their coolant leaks

I posted yesterday about the '91 318is I was looking to buy.  This is
the last year of the E30, with the new twin cam four that's still in
the 318's.  Well, I bought it today, in spite of the warnings I
received about the coolant occaisionally taking a different route than
the rest of the car.

As I understand it, there is an O-ring that seals a coolant port from
the block into the head, forward end.  Normally would be within the
head gasket, but for some reason they used this O-ring.  Corrosion in
the head's aluminum, under the O-ring seat, can eventually allow
coolant to get by the O-ring, resulting, naturally, in loss of
coolant.  The local BMW dealer says to expect it every 50k miles!  It
may be visible as a trickle off the right front side of the engine
before things get too far along, but it sounds like most people find
out about it the hard way!

BMW changed the design in 1993 to fix this, according to the local
dealer.

The cure is to remove the head, fill in the corroded part with epoxy
goop, clean it up and put it back together.  $700 at both the dealer
and the independent shop where I learned most of this.

The best thing is to make sure coolant is changed regularly, which
cuts down the rate of corrosion.  I've heard of examples of this car
going 100k miles with no trouble.  I intend to start changing the
coolant twice annually, in hopes of staving this beast off!

I'm still interested in any other info out there -- I haven't received
anything very informative yet.

Jim Newman
'91 318is (purchased today!)