Q: I just bought this car and engine code came up for the camshaft sensor bank 1

So I just bought this car and I had a engine code come up as a camshaft sensor for Bank One I took it off cleaned it up and clear the engine code and then I tried to start it and the code did not come back up it stayed clear and then we took out the spark plugs and they were covered in oil so we did a valve cover gasket replacement on both sides now we tried to start it up and it would not start so we started to do a compression test for the spark plugs we took the spark plug out of the left side closest to the front of the car we did not get any compression we left the coil pack out with the spark plug sticking out of it so we could see if it had Spark , we turned the key to test for spark and it started but very very weakly it barely ran the RPMs barely went above the first - and then if we tried to give it any more than an inch worth of gas it would die out so now I'm just trying to figure out why it would start missing 1 spark plug and having an exposed cylinder

My car has 120000 miles.
My car has an automatic transmission.