Should be able to feel with your finger, or a small dental type mirror and torch is a good tool to see closely.
Sealant on the Oring is to be kept to a minimum and is only if you have to reuse the old one, or can't get the correct section. A small amount of Wurth 250, Permatex Ultra Blue, or similar oil resistant product will be sufficient.
DO NOT use lots, and none in the bore where the seal sits.
What was the seal number you were supplied with?
JC

