I've taken apart and fixed a couple 98 Beetle latch assemblies last year. For what it's worth, you can use a later Mk4 latch module in the Beetles, you'll just lose the characteristic loud "ka-chunka" lock motor setup. There's a spring loaded buffer of sorts in the newer modules that makes them quieter and is geared a little different.
One of the 98 modules I saved last year had a contact corroded away completely. So I literally frankensteined a lock assembly together using the circuit board and microswitches from a later lock module and the gears and motor setup from the Beetle.
But realistically, you don't even have to do that. A newer module is plug n play. They're wired the same. Not very complicated devices, really. Just a handful of simple microswitches and a motor assembly.