What should I be checking/looking at/cleaning/replacing/crying over?

I searched the forums but didn't get any straight answer, just some troubling hints that a strong gas smell was a precursor to the engine dying...which I would really like to prevent.

Any help would be appreciated. I have 143k on the clock, I just did an oil/filter/PCV change at 140k and put Castrol 10W-30 High Mileage Semi-synth in. I replaced the grommet the PCV valve sits in because the old one was rotted/torn right at the neck (got 2 for $12 from some online place).

Any advice appreciated. I want to nip this in the bud if it's major.

-Tom