My 47 Commander developed a port transmission oil leak. I think its the rear seal but not yet 100% sure. Its a tight squeeze getting in there and just curious if anyone has any tips to replacing it to make the job a bit easier?

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Try some AT205 stop Leak first. May buy you some time. I was not a believer that any stop leak really would work but after reading the reviews I thought I would give it a shot on my paragon  trans leak. After a few hours or running there’s hardly any oil on my oil pads.  

Thanks for the suggestion but I want to repair it rather than a bottle of fix. I do charters on the boat and I cant afford it to dump out a bunch of oil again on a 20 min cruise to the island. I had to disconnect the bilge pumps to prevent it from dumping overboard. It was a nasty mess to clean up.


I would be looking at the two hoses that go to and return from the main heat exchanger. These are more prone to leak with age then the rear output shaft seal, especially if you have a sudden increase in leakage. They are located on the bottom of the heat exchanger. The hoses tend to fail at the fitting or wear the hose might rub. Usually a small pin hole leak will develop before total failure.

The rear seal also will throw oil around the engine room which I don't see in the picture.

Hi Bill:
I agree with Ron on his assessment, however permit to add one more possibility.
That is, that on the 506 there were originally two (2) short and narrow diameter “crossover” pipes on the very top of the marine gear that were prone to cracking and leaking. Our stand one let go on our original delivery trip from FL to NY. Mechanic suggested going with high pressure hoses and soon thereafter did the same with the Port. He explained that since the 506 operated over 325 PSI those original pipes were prone to break because they were made of aluminum. Problem solved
Best Regards,
Jim Rivas

Thanks Jim and Ronald, I will go take a look at it in the morning. I have not had a chance to work on it yet but will tomorrow and let you guys now what I find.

I finally had a chance to go down and find the leak. Not good. I added 1 gallon of oil started it and it was poring out the real seal. The pic is after I shut it back down.

Anyone ever changed out the shaft seal before? Looks really difficult to get to.

Hi Bill:
I feel your pain on this one. The pic clearly shows a bad rear seal. The question now becomes as to fitting a temporary framework to hold up the marine gear while changing out rear seal. I have seen this job done on a number of boats equipped with DD 6-71N engines since they also used the 506’s. The problem will be getting in there with the crossover exhaust pipe in the way on your V8 since the 6’s did not have that pipe to contend with. Very good possibility that it may have to be taken off for better access. I personally have helped changing out a rear seal on a 514 Twin Disc and that job was a royal PITA. Good luck to you on this project and let us know your progress.
Best Regards,
Jim Rivas

I was able to lay down on the port side of the engine and replace the seal without too much trouble. Seal was less than $20. It all went back together with no issues. Took the boat to Gasparilla Pirate Invasion yesterday, 4 hour cruise each way. No leaks. I also inspected all the hydraulic lines replaced sea water impellers and fixed the water leak, cleaned up the rusted area and all is well now. Thanks again for your suggestions and comments.

So glad to have her back up and running.

Daily charters are back up and running.


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