Sounds completely normal. Perversely, having bought a new relay for my rebuild (new chassis), the relay slipped straight out of my old, holed, rusty chassis (all extremities, including dumbirons, had been replaced). No seized or even stiff bolts, no bashing with a hammer, heat or levering; it just lifted straight out! Of course, had I planned to re-use the relay, things would have been different...
Stage 1; spray a liberal amount of penetrating oil around the top and bottom of the relay and let it soak over night.
Stage2; use a crow bar to lever the relay bolt flanges away from the top of the cross-member.
Stage 3; use a blow torch to heat (not cut) the cross-member's relay locating hole, then, while still warm, bash the underside of the relay with a big hammer.
Stage 4; swear, curse and go to stage 1!
Stage 1; spray a liberal amount of penetrating oil around the top and bottom of the relay and let it soak over night.
Stage2; use a crow bar to lever the relay bolt flanges away from the top of the cross-member.
Stage 3; use a blow torch to heat (not cut) the cross-member's relay locating hole, then, while still warm, bash the underside of the relay with a big hammer.
Stage 4; swear, curse and go to stage 1!