My friend has an Impala with a 383 in it. He was racing his dads Camaro and over-revved it trying to keep up and threw a rod. Well he got the engine rebuilt, bored .030, etc.... After about2-3 weeks it starting smoking out the left tailpipe only and oil pressure dropped to almost 0 at idle, and went up to like 20 @ WOT. Took the head off the left side of the engine and one of the pistons had about 1/4 of it broken right off. The car still had a lot of power and ran good, other than the smoke. (it was about 550hp to begin with so it still got up and went) It could easily be something like this...but doubt it...just giving you an example of something that might cause that.
Seeing that you said it was driven hard, I would bet it something internal, and not like the oil pump or something like that. If driven hard, 30k is a lot on a rebuild.
And, IIRC didn't '84 Camaro'* have 305'*?
1990 Maroon Grand Prix STE McLaren 3.1 Intercooled Turbo, 14.695 @ 94.49 on 12psi before cam/heads/etc.
1990 Bright Red Grand Prix McLaren 3.1 Intercooled Turbo, 14.819 @ 92.72, 189whp
1999 Grand Prix GT 9.75:1|K&N|160 tstat|No Ubend/Cat/Res|UD Pulleys|Ported M90/TB/Heads|XPZ|2.55"|Pacesetters|Stage 2 I/C. 12.442 @ 112.78
2000 Blue Bonneville SSEi Supercharged Gutted Airbox|K&N|3.4"|1.9'*|WP Pulley|Custom DHP|180*stat|41932'*|No Cat. 14.681 @ 94.80
2002 Dark Cherry Grand Prix GTP Supercharged & Intercooled
12.084 @ 114.38 w/1.743 60', 315.6whp, Fastest Stock Cam M90 GTP!
NOW XP CAMMED, 340.6whp with XP, stock heads, Gen 3 M90, 11.984 @ 115.84 w/1.750 60'!
Most HP Stock Heads Gen 3 M90 GTP!
2004 Red Monte SS Supercharged K&N|3.4 Pulley|1.9'*|180*stat|41919 plugs|3" dp|No cat/ubend|DHP|Shift Kit. 14.2 @ 98
GOT BOOST??? Friends dont let friends drive stock!