On my ’55 Customline with the T85 3spd OD tranny, I was able to install two seals back-to-back in the seal hole for the overdrive solenoid.  Did that over twenty years ago and it’s been leak free ever since.

Lorena, Texas (South of Waco)

Thanks to both of you for your advice.  Although my O.D. stopped working because the solenoid was pretty full of oil, I cleaned up the solenoid and it is now working again.  I found the seal on Ebay for under $10.00 including shipping.  
https://www.ebay.com/itm/295624150159

Dearborn is right. Mac at Van Pelts is active on these questions at least at the Ford Barn and the HAMB. If you don’t find it or have questions using the on line catalog, call.

http://www.vanpeltsales.com/

miker
55 bird, 32 cabrio F code
Kent, WA
Tucson, AZ

Daniel is correct, the seal in the trans can simply be carefully pried out. That seal should be installed with the open/lip end to the inside of the trana. As far as the solenoid, if I can remember correctly, it too can be removed from the outside as I don't think there is any way to get at it from the inside because the coil winding is pressed in to the housing. - been too many years.  The seal in the trans used to be available from a good bearing supply store but you will need exact dimensions of the bore and shaft - not a big deal.  Not sure where to source the solenoid seal. Try Vanpelt for both and if that doesn't work, I may? be able to come up with a number for the trans seal.

64F100 57FAIRLANE500

Changing the trans seal is simple. I use a short length of wooden dowel to insert, in order to keep most of the fluid from running out. Only issue, is whether one side of the replacement seal should go up, or down (haven’t figured that out)?. I don’t think the parts diagrams/drawings are that detailed (?).  Also, I make sure the solenoid drain hole is pointing down when reinstalling. If the new seal doesn’t leak, then likely the solenoid inner seal’s competence is moot.  If you DO disassemble the solenoid, then there are various other relevant/opportune maintenance tasks while it’s apart.

6 VOLTS/POS. GRD. NW INDIANA

I have transmission fluid leaking into my O.D. solenoid and it may have caused it to fail.  It sounds like there is a seal in the transmission and one inside the solenoid.   I don't know which (or both) are leaking.   As to the seal in the transmission is it installed from the outside by just pulling the old one out with a hooked probe and pressing in the new one or does the overdrive have to be apart to change it?  From what I read online, it does sound like the one in the solenoid is more difficult to replace.  Thanks