Applications include these engines (and the boats that we are aware used these engines... There could be other combinations as well):
• M-12 (Catalina 25, Capri 26)
• M-2-12 (Catalina 25)
• M-5411 (Catalina 27, Catalina 30)
• M-25 (Catalina 30, Catalina 34, Catalina 36)
• M-25XP (Catalina 28, Catalina 30, Catalina 34, Catalina 36)
• M-25XPB (Catalina 28, Catalina 30, Catalina 34, Catalina 36)
• M-35 (Catalina 34, Catalina 36, Catalina 38)
• M-35B (Catalina 34 MkII, Catalina 350, Catalina 36 MkII)

To quote Universal's Operator Manual "Universal engines use a replaceable air filter element wrapped around a metal canister. This element can be removed and brushed off or cleaned with an air hose. When it becomes too contaminated, it can be replaced. The canister with its interior element should also be removed and cleaned periodically. Simply wash the assembled unit in nonflammable cleaning solvent."

To operate efficiently a diesel engine must intake a continuous volume of clean air. Hard starting, an erratic idle, and black exhaust smoke are all symptoms of a restricted air intake."

In practice, we find the heat of the engine in its enclosed compartment accelerates the degradation of the foam. It is not unusual to find the foam, stiff and baked by the engine, crumbling into small shards that are being sucked into the engine. The element, designed to protect the engine, is contaminating it instead. It is probably long past time to clean the canister and replace the foam element.