My experience with those tubes is that they only fit tight once.
I am not sure I know what you meant by this. I could interpret it to mean the original tube would only fit tight once if it was to be reused, or could mean the hole in the transmission case could get enlarged, so even a new tube would not fit tightly.
I can still see factory cross hatching at the base where it press fits in place and also some areas with factory paint still in tact, so I am assuming the bore in the case may be slightly enlarged. Perhaps partially due to the fact that the dipstick tube was not bolted in place from previous mechanic and vibration worked it loose.
I had one transmission guy tell me he JB Welds the tubes in place when they leak.
Would I be better to JB Weld if the case hole is slightly enlarged to bring it back to a tight fit, or go with the Ford Grey RTV to gasket seal it? Perhaps even hylomar blue?
I will be able to see this from the bottom with the pan removed, so I can be sure that there will be no contamination into the transmission or fluid, and will be able to clean all the surfaces well.