The sensor sounds like the over pressure sensor. It is located just behind the bell housing on the drivers side. It is the first thing down that side and measures the pressure at the band servo. It causes the timing to be retarded to relieve the force.
If it was patched I would definitely replace it.
As to the leak and hum, I would check your PS fluid as the pump is on the left front of the motor and the fluid looks a lot like engine oil.
For some reason most of the oil leaks we have fixed have been on the passenger side. If you are low on PS fluid it will moan and groan.
Bosch Master, ASE Master, L1
33 years MB technician