The yellow thing you circled is an oil distribution manifold. The black thing towards the bottom of the pic is the 15PSI oil pressure switch, and the bottom edge of the oil pressure gauge sender is just visible pointing up behind the power steering pump. Nice pic of the green air compressor support bracket, don’t let that get loose
Should just be a paper gasket between that manifold and the block. First thing I would do is make sure its bolts are tight. Then that all the things connected to it are also tight. If that doesn’t fix it, disconnect the sensor wires and you should be able to remove the manifold with sensors to renew it’s gasket. While you have it out remove the sensors and put a little pipe sealant on their 1/8” NPT threaded ports…
As mentioned, sometimes the sensor failure mode is to leak oil, so it could be a bad sensor. Only way to really determine this is to clean it up really well, then start it up and watch it… Another method, is after a good cleanup, tie a short strip of white rag around the fitting on each sensor or tap to see where the oil builds up…
The crankcase vent hose also hangs in this area so oil in this area from blowby gasses on the starter and inside of drivers frame is not uncommon, and a pain to clean up. I pulled that crankcase vent hose up and over the frame in front of the power steering reservoir so the end hangs outside the frame rail. You can see it without raising the cab and any oil residue is outside the frame away from the starter and all the hoses and wiring that run along the inside of that frame rail…
I am still cleaning out oily residue in that area from when I picked up the truck from auction…
