I have an old hydraulic toro Custom sprinkler controller. The drain lines seems to be
getting water from the control supply line. Is it possible this leak is due to some seal
breaking that can be fixed by disassembling the controller ? Or is this a big headache
that isn't worth the time.

I found the drain leaking while trying to find where the control (supply) line goes. The supply
line doesn't have enough pressure to keep the valves closed (off) so I'm trying to find
where the line comes from and plumb a new line to clean that one out...
(Unfortunately, the lines don't seem to terminate in an easy to locate box in the yard.
[I haven't found it with all the poking around I have done.])