The source version of ST resides on the host capo.private.uwaterloo.ca, in /software/rt-math-1.
There is one program written in C
(/software/rt-math-1/servers/st-suid-perl).
It's a setuid cover for the rest of ST, which is written in Perl.
The source resides in
capo.private:/usr/source/rt-math-1/st-suid-perl.
It's extremely rare to need to change it.