YODAONE

After 20+ years, a fair amont of sediment accumulates into a greasy muck in the starter valley area underneath the intake manifold.

Recently Extrude-honed and swapped out my intake and found s 1/2" of goop in bottom of valley...requiring one hour of cleaning...

First, this accumulation inhibits cooling, second...the goop may (either it does or doesn't ) dampen upper block, thereby inhibiting the function of the knock sensors in proximity.

In any event , nothing lost by cleaning this accumulation under the manifold...a few $ for gaskets...be sure to use pressurized air to disperse sediment around intake to heat ports before lifting intake manifold.

dicer

And sometimes the mice love that area for nice flammable nests.

YODAONE

Used plastic'-scraper, one roll of paper towel, blue body shop masking tape to cover cylinder head intake ports, two old tooth brushes, one large can of Gum-out and one large can of CRC (red can) brake cleaner.

While you are at it....look into cylinder head ports...good time to clean carbon buil-up from valves and ports....can use the carb cleaner...DO NOT spray down port, but apply to toothbrush...too much fluid into port while engine nit running may cause hydro lock...Let everything vent for 24 hours before starting.
Ditto for runners on your intake manifold.