Pinballlife.com sells flipper rebuild kits In pairs or you can just buy a left or right. Maybe order 2 rights, a left and the respective coils?

https://www.pinballlife.com/williams-flipper-rebuild-kit-041969-to-121979.html

I would do the 3 personally. I have owned the game, and worked on the flippers extensively. The 3rd flipper is a key to this game, and you want it to have decent power.

*HOWEVER*

Before ordering a rebuld kit, I would recommend attempting to clean up and get them working as best you can to being with.

At worst, you become more familiar with the assembly, so you can set up the rebuild better. You may also find other underlying issues that require attention i.e., maybe there is no sufficient voltage.. who knows.. you really need to try to get it working before just buying parts, or you could end up throwing an inordinate amount of $ at the machine

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At best, you may find that you can get them working fine, as what I did. The OE set up is not the best, but can be fine for the game, particularly if you replace the bracketted flipper assembly with a pure plastic flipper.. it reduces weight and makes them a bit snappier.

If I were going to throw money at flippers, I might consider the WPC flipper mod that you may find much infromation on this site about.