If I understand correctly, the couplings of the longitudinal component of the $W$ and $Z$ bosons should be "equivalent" to the Goldstone bosons they ate after SSB.
In practice, this makes their interactions with fermions dependent on their mass over the mass of the W boson. I believe the idea of this is stems from some sort of manipulation involving the Dirac equation, just like this presentation does it: https://indico.cern.ch/event/288811/sessions/54831/attachments/538857/742841/Sreerup_Higgs_Physics_II.pdf
How can this be achieved in the context of loops. I have found some old papers that use this to explain a non-decoupling of top quarks in radiative corrections of $Z\rightarrow b \bar{b}$. For example:
https://arxiv.org/abs/hep-ph/9307295
https://doi.org/10.1016/0550-3213(91)80023-F
Which, I guess makes sense if I blindly accept that I can substitute the longitudinal part of the $W$ boson inside the loop with a Goldstone boson in t'Hooft's gauge. But what if I do this in the unitary gauge, then the mass dependence is not clear? The only sources I could find on this make their claims when the $W$ bosons are on-shell and also if the fermions interacting with the $W$ are also on shell. In this case the top quark is inside a loop and so is the $W$ boson, it is no longer clear that the longitudinal part of the propagator is proportional to the mass of the top quark.
