Hi Gibbo,
If you have stripped the forks down and are wanting to soak the foam seals in something then Fox / Mojo recommend cleaning the rings in the same suspension fluid that is in the legs and then coating with fox float fluid.
If you just mean what to use after you have cleaned all the mud off the stanctions then Fork juice is good i’ve heard. TF Tuned recommended finish line Dry chain lube with Teflon and thats what i use. Clean the stanctions then put a line around the stanction just above the seals. Pump the forks 20 times then wipe the muck away.
hope this helps