The suggested labour cost seems "too" reasonable to me also.
Assuming the '98 is not too different from my '99, there is a 4-piece sealing system under the lower intake manifold;
... 2 pieces of gaskets between the two heads and the lower intake manifold. These gaskets pass intake-air and coolant.
... and 2 end "seals" at the front and rear of the engine block, between the block and the lower intake manifold.
It sounds as though the front seal is at fault. If it leaks oil outward, it probably leaks air inward ... and helps to account for the condensation you see around the oil cap.
If you can live with the oil leaks, I would wait until the air leak got bad enough to cause MIL codes. If Blackstone finds significant coolant in the oil, that's a different matter ... and you will have to assume you have more that just water-condensation getting into the crankcase.