Mark 55 end cap seals confusion

I am trying to resurrect an old mark 55 and in the process decided that it was long past time to replace the 60 year old end cap seals. I did the lower one some time back without incident and am now getting around to the upper. I have removed the seal and bearing and was about to put the new seal in when I noticed a hole in the metal portion of the seal that is not present in the old seal. According to my parts book, the correct part number for this seal is 26-29476 which has been superceded by part number 26-41953, which is the part number of the seal I have. I am having trouble understanding how crankcase pressure is maintained by a seal that has a hole in it and before I put this seal in and button this thing back up, I wonder if anyone can explain why the seal has the hole. I don't recall a hole in the lower seal when it was installed. There are instances where a hole is present in seals, but I just can't see the logic for one in a two cycle outboard crankcase. Can anyone help me with this problem?

Do not use the seal with the hole in the UPPER position.---------------That was only used in the LOWER application.-------Somehow you have gotton the wrong seal.-------Run to your dealer and exchange it !!!

Thanks for the speedy reply. I'm still a little confused though. The part number for both the upper and lower seals are the same. I would expect a different part number from the upper and lower if there is a difference----? Since there must be crankcase pressure for a two cycle to operate, why would there be a hole in either seal?

??-----It was used in the lower application where one seal had a hole to bleed out oil.----------Run to your local dealer to get a 26-41953 and it will not have a hole in it.--------No point arguing this.