With regards to a diesel combustion 4-stroke engine, what are the causes for leaking & holed suction / intake valve on cylinder head?
Appreciate your valuable advice & feedback.

It is very unusual to have that sort of problem on the inlet valve.

If the inlet valves are fitted with ROTOCAPS, are they working?
are the valves fromthe original engine maker or a substandard supplier?
is their a major problem with valve or injection timing, or valve clearance so that the valve is partially open during combustion?
where the valves correctly overhauled?
Thats all I can think of for now.

BP

Check the pressure drop across the air cooler. Cleaning the air side of the air cooler should help.