I put a vaccum gauge on the fuel line and when the pump starts pulling near 3" hg., I change the filter. No point changing a $10 (or more) filter till it needs it. When there is enough pressure to push oil out the dipstick, it can also push seals out. I saw the I-shaft seal pushed out on the engine previously mentioned and wondered why ... till I got the engine in and started.
I could see a small hole in line with the vent. Is this what was drilled out?