I have a slow oil pan leak from the back of the pan when the engine is running in a marine diesel. The engine is sloped to the rear. It would be a major job to lift the engine in order to change the gasket. Is there any product I can use to put on the outside of the back of the pan that would stop the leak? The engine bell housing forms a small channel between the pan and the housing of about 1/2 inch. Is there some product that I can sgueeze in that channel that would adhere to both the housing and the pan and would withstand vibration?

If the leak is slow and it doesn't present a hazard to where it leaks don't sweat it. If you must, make sure the surfaces are cleaned then try JB Weld. I've never used it between a pan and block, but have fixed leaks in oil pans with it. Easy to apply but will take your rig down for a day because it takes a day to fully dry.