Need some help with Brake issues

Yep. Like Bob W says.
The Brake light should be illuminating, not the Oil light. Separate wiring or connector issue. That may have always been crossed, but never faded the pedal to trigger the switch.

As for the pedal fade, The core of the latest M/C could be bad, or the bench bleed connectors sucked air.
Why don't you get your original rebuilt? DIY or ask around, That will correct the original leak.
Nothing terribly tricky about rebuilding MCs or cylinders, but can be messy. Basically it's honing the cylinders and installing new rubber seal kits.
Then check for leaks, especially at the rear brake cylinders, and bleed the entire system. (keep the rear drums on when pumping the pedal, easy to forget and blow the cylinders apart).