Screw threads seized on bike rack

[GoatBoater]

I live near the coast and salt eats everything around here. The threads on the bike rack screws have completely seized up as a result.

I've been trying to get penetrating fluid in there, but they're not budging.

Can anyone offer any advice on either: how to free them or where to source replacements?

 

[Scottish Scrutineer]

Use heat to assist in releasing them. A hot air gun, or small blowlamp may work, or even a big old-fashioned soldering iron.

If you can replace them, use stainless steel and coat threads with Duralac to reduce the galvanic corrosion