The LU on those motors use grease. Lubriplate 105 will work but I find it a bit thin so I use something a bit more substantial like John Deere corn head grease or equivalent.
There are screw plugs in the LU I believe but to clean it out good I would remove the prop and prop shafts cover.
As a side note, you may want to check and make sure you don’t have grease in the water pump piston. The piston can wear and allow grease to get by and gum up the pump.
