When I pulled off my stock intake manifold at 5k miles (cobra jet) the cylinder head intake ports in all 8 cylinders had a nice coating of black sludgy oil covering them. At 3k miles I deleted my PVC with breathers. So that build up was only from that amount of miles. I obliviously wiped clean the ports before new intake install.
Why do you run catch can or breathers? Over time (12 mos 3k miles for me) the oil build up in the intake and intake ports will effectively lower the effective octane in the fuel you use causing detonation and pinging. This is proven cause and effect in any highly carbonated motor. Excessive detonation breaks piston rings and you know the rest. Additionally the breathers help ventilate crank case pressures and highly acidic vapors (fuel/oil) out of the motor.
The PVC system was designed for EPA regs and not exactly beneficial to your motor. To each his own...
How much does a nice coating
(of sludgy oil) equate to? At this relatively low mileage that's a little concerning.