Anyone know if there's a source for a replacement dip stick seal. This is for the one fitted into the umbrella cap of the dipstick to seal off the top of the tube. My searches yield seals for the bottom of the tube only.

I don't remember there being a seal at the top of the tube but I really never looked.

Mine (68 727) has a black rubber plug about 1/2" tall molded with a slot for the dipstick and appears to have been cut vertically on one "edge" of the stick to open up and close back around the stick, sort of "c" shaped piece that closes shut when pushed up into the cap.

To my knowledge, that seal was never offered separately, it's considered to be part of the dipstick assembly.

I may have to spring for the smallest most expensive seal (buy an assembly for the thing)!

I have a NOS trans dipstick for a dodge van. You could take the seal off of that to use on your stick.

Problem is, it's not as easy as just slipping on a new seal; the rubber seal at the top of the dipstick is retained by a steel washer that's held in place by staking the dipstick. Not saying it can't be done but it's not a simple slip-on.

nos stick

I took a good look at mine. The raised collar is there only as a short remnant, appears the tube riding close to an after market header ran it hot enough to shrink it, and likely harden the rubber causing it to shrink and fail.
The metal "cap" of the dip stick is loose enough to slide up and around the handle (round finger hole) of the stick allowing the plug to be slid onto the stick above the washer and the cap returned, and the shape of the handle restored.
This can be accomplished IF a new rubber plug is flexible enough to slide around the handle and over the swedge that retains the cap in place without damage.

If the swedge that retains the cap isn't intact, the cap can slide up and your level readings will be off.

I got it.
The original cap has just enough wear it can be tilted and worked around the swedge. After reinstalling a slight additional swedge, or squeeze with clamp or cushioned plier will keep it retained.
Another of the little problems these old cars present.
I'm more curious as how to get more clearance so the melt does not re-occur.

May not be the route you want to go but I put these in everything now...Not a drop of transmission fluid on the floor ever...

https://www.summitracing.com/parts/lok-td-3727fm/overview/

while i like the idea of a flexible tube, those lokar deals upset me because of the small internal diameter of the tube, and the length of time it tales ME to fill the transmission ! your mileage may vary.

And the fluid level is hard to see on the stick.

I bought one of these: http://www.manciniracing.com/man727diptub.html. My local track (Tulsa) likes to see the locking type even on the slower cars.

With great help from mopars4ever I now have what appears to be the correct seal for my original. I'll be massaging it together in the near future.
Thank everyone for suggestions and help!