Will intake manifold leak cause low compression on 6 cylinder?
NO! You could run a compression test on an engine with NO intake
manifold installed, so a leak of any size will not affect
compression. The only things that usually affect compression is
your rings, valves, and valve timing. if you have low compression
on only one cyl, then valve timing is probably OK. With the piston
at TDC removed the spark plug and introduce low pressure air
(20psi) into the cylinder. If rings are bad, air will go into the
crankcase (air comes out the oil cap), if air comes out the intake,
you have an intake valve concern, if air goes out the tailpipe, you
have a exhaust valve issue......Good Luck