The sensor is gripped by a spring type round thin steel tube and it's usually a bit stiff to pull out.The densor body is stainless steel (a) because it's non magnetic and (b) it's rust & corrosion proof. That said, the position of them leaves them open to dirt build up.
Suggest you give it a good soaking of either Plus Gas or, failing that WD40....really soak it, it will not damage the sensor, and leave it to work. If there is sufficient height protruding, tighten a suitably sized Jubilee clip onto the sensor and using Vice Grips try rotating the sensor to & fro whilst trying to pull upwards..if needs be give it another dose of WD40 to flush the muck out. Do NOT pull on the cable. If there is insufficient room to fit a Jubilee clip then try a suitable pair of grips but do not apply excessive pressure which will deform the sensor body.
The secret is to get it moving.
Before refitting, clean the bush and coat the sensor with Silicone grease...press the sensor in until it touches the reluctor ring on the CV joint.