When replacing the impeller in a raw water pump on a diesel engine, that is
sealed with a paper gasket, is it necessary to "paint" the gasket with silicone
or some other type of sealant when replacing the cover?

Also, I've heard that coating the impeller vanes with any kind of petroleum
based product, like Vaseline, ( to ease the installation) could cause the
neoprene vanes to swell or otherwise be damaged. Is this true? What about the
use of ordinary dishwashing liquid?