I have a 1971 Johnson 4 HP that runs like a dream,but I have water /oil mix in the lower unit . This motor doesn't have reverse . How difficult is it to change the seals ,and which one is the likely culprit ?
It might be as simple as the seals on the drain and vent screws. Try new ones with new oil and see. Next suspect is the seal under the water pump. Fishing line on the propshaft can and will damage that seal.
Performing a pressure and vacuum test on the case will reveal the culprit
Difficulty? depends on your mechanical ability and what tools you have. Get a service manual
Those are about as simple as they get. One seal under the water pump. Another on the prop shaft, with an o-ring around the outer lip of the propshaft carrier. A gasket apiece on the two drain/vent screws and that's it.
