What's strange is it came out of the blue after 30 years. This is an all street car and not really abused so I don't know how the pickup could crack but never say never
No external pickup hose? This should not be happening, with any half decent filter. Try a NAPA Gold.
Once you've tried a few filters and nothing changes, then we have to consider it's internal.
If the results don't match the theory, change the theory.
