CO2 regulator + solenoid question

I am looking to piece together a calcium reactor for my 150 as it will be an SPS tank. I found a good deal (I think) on a CO2 regulator with solenoid but the original owner says the solenoid sometimes stick. He cleaned it 6 months ago and it started to stick again so he just got another. My question is, can I do a "better" job cleaning it somehow to keep it from sticking or is it shot once this issue starts? If it is shot can I replace just the solenoid or is it all or nothing? If I can/need to replace it, how much would it cost? Brand new it retails for $150 and he is willing to sell for $35. I have never seen a price like that as even used sell for upwards of $75. Just wondering if this is truly a good deal or if it will most likely cause more headache than it is worth. I have seen pics of the unit and there is no visible rust or damage, and the only thing the seller mentioned was the sticking solenoid.

 

Should have mentioned that, it sticks closed so that effectively there is no co2 being pumped into the system.