Hi,and welcome to FF,
( general advice--as I've no idea what engine / spec you've got)
the sumps are generally sealed with a FIAT type of "mastic / sealant",
YES- it will feel "stuck-on", when changing rusted-out steel sumps,
the sump is often in pieces by the time the sealant "lets-go"..,
so if trying to remove a cast sump for internal mechanics.. be WARY,
Charlie