#5 cyl. I-5 typically has a problem=clogged exhaust manifold?

[Nathan Belo <belo@eskimo.com>]

Car:  1988 90Q tornado red, NG = no good ;) engine 
Mileage: 181K+
Problem: No compression #5 and burning oil
Solution: Pull head and bring to machine shop for hot tank, valve job,
head surfaced, etc.

Condition of head: All valve guides evenly loose, no broken/bent valves,
no burnt exhaust/intake valves.  ***Exhaust manifold #5 is supposed to be
about a 1.25-1.5" diamater, but it was so coked up with carbon there was
barely a 1" dia. hole***  3 hairline cracks between valves that didn't
seep into the valve seats.  Machine shop said this is common with the
aluminum heads and not too worry unless it was seeping down into the valve
seats.  For an additional $200 they could weld the cracks and put in new
valve seats.  We're just bolting it back on.

Hungarian VW factory trained mechanic for 30 years (Rabbit Service on Lake
City Way in Seattle) says the pistons are fine.

I heard a rumor that the #5 cylinder typically doesn't get enough air and
runs lean.  Is this true and would that explain the clogged exhaust
manifold?  

Nathan Belo
'88 90Q