Info on 2000 johnson ocean pro 200 HP.

[rat"BASS"tard]

Im looking at a 2000 26’ striper with a Johnson 200 ocean pro motor
And upon inspection of motor I notices that (looking at the motor) the
Left bank seem to have a salt water leak at the top of power head.
All of the ends of the plugs going into the cylinders are rusted and on the rt. Side they look fine there what appears to be a sensor with wires coming out of it at the top of the head and im thinking this is the source of the leak. Can anyone tell me what this is and what it dose.
I will be going back in a week to run motor and do a compression test
On it as well what is min. expectable compression for this year motor
Seller states very low hours on motor and boat and at first inspection
His statement appears to be true (boat & motor are very clean)
Thanks