For 1981 to 1984 300D 300CD 300TD 300SD and some 1985 Federal Models without Trap
These two small o-rings seal the oil drain tube that goes from the bottom of the air filter into the engine oil pan.
617 Turbo Diesel Air Cleaner Housing Oil Drain Tube Seals
$2.95
SKU:
DSL-COMTACDS 
Product Details
When these o-rings are damaged or missing the tube will leak oil and / or will rattle. One o-ring is placed on a nipple coming out of the bottom of the air cleaner housing and the other on a nipple coming out of the engine oil pan. The top o-ring can just be changed by removing the air filter housing, but the tube bracket (backside of turbo) must be removed in order to pull the tube off the bottom nipple for o-ring replacement.