If you look at the schematics for the VT-100 (which are available on bitsavers) as well as most terminals of the day used the Motorola MC1488/1489 driver pairs [early on, TI marked them as 75488/75498 but I doubt you'll see that old].
Anyway, for any terminal of those times, I'd be surprised if the later devices (like VTx20 series) did not them [the issue with these devices is you need all of 5 and +/- 12 volts]. These terminals are new enough that they might have used MAX232 (single 5 v power - there are even 3.3v versions these days). All of these devices are very available online. I would suggest putting high quality (i.e. auget style / machined pins) sockets. The nice thing about 1488/1489 is that they were doped to fuse the output section on failure, so just replacing them will in fact resurrect most serial port failures. Frankly, I never understood why more manufacturers did not put them in sockets for easy replacement.
That said before you open up the case, I make sure you are cabled correctly. If you are using so-called 3-wire cables, then you need to ensure RTS/CTS [4-5] are strapped and DSR/DCD/DTR [6/8/20] are also strapped. The terminal will ignore any I/O unless it sees these pins asserted.