Now that the head is back on, do a compression leakdown test. If you have significant leakdown, the rings will have to be done. I don't know how the plugs can be "sprayed" with oil. What do you mean exactly? The top compression rings if good should prevent major oil from getting into the cylinders. Oil control rings are designed to trap oil from below and inside the pistons and provide lube to the cylinderwall/piston interface. Are you confident that the work on the head was done by the book. What parts were replaced, i.e. seals, valve guides, etc. what was the mileage and why the rebuild??
1987 BMW 325