Janie, it is quite possible that all you have is a loose spark plug wire. It will make the engine miss and it will activate the check engine light.
The oil leak, sounds to me like when it reads low maybe you didn't push the dipstick all the way in, and when it reads full that you did push it in.
I have had good luck with BARS LEAK for a leaking rear main seal. It's very common in antique cars.Much cheaper than having the seal replaced.
Whoever told you that it cant be stopped should take up knitting.