Fix for faulty Modulation Generator

[NoNotDoomX]

This is my first post, so hello everyone!

I recently found a problem with the modulation generator on my 6 year-old MS-20 mini: the knobs labeled "MG/T.EXT" do nothing. The LED light flashes, and I can adjust the flashing speed, but there is no audible difference when turning the MG/T.EXT knobs. I don't know if this has been a long-running issue or a new development because I hadn't played my unit in a while when life got in the way of music for a bit, and I had trouble wrapping my head around modular synthesis even when I was playing it all the time. I took my synth to the only authorized Korg technician in my area and he said some component on the MG board is bad, but everything else is in absolutely perfect condition. Unfortunately, the only replacement board he could find is $600, which is ridiculous

This brings me to my questions:
1) Can I just patch from the MG to where I want it to modulate (the LPF, for example) and get similar functionality as turning the MG/T.EXT knobs?
2) Can I patch in a separate LFO to act as a new modulation generator and where should I patch it in to get similar functionality?
3) I also have a Monotron Duo and Delay; can either be used as an LFO?

Thanks!