Often the dog house oil cooler air ducts are put on carelessly (or missing the lower pieces). Here's photo a a well sealed complete one - even uses foam to ensure good seal. Is the Hoover bit missing in photo? Ha, doesn't look like spark plugs seals are sealing as well as they could (probably old rubber seals).
On diagrm below it looks like #9 and # 10 are missing - might be what Al refered to but his diagram doesn't show up for me. They are easy to add. My engine has a rubber sealling ring around the hoses from shroud to heat exchanges where it goes thru the rear breast plate (to prevent exhaust gases from being re-ingested and sucked back up)