The 51130-17GB0 is for a K8 (R). A K6 uses a 51103-17G00 (RH and shares it with K3-K7) and a 51104-17G00 (LH and shares it with a K3-K6), according to Fowlers.
https://www.fowlersparts.co.uk/parts...7/front-damper
Regarding the S360 number, I found this:
https://www.boonstraparts.com/en/par...l/000000237945 it is a K4 (L). If Fowlers are to be believed then it is actually a 51104-17G00 since it's the same for K3-K6.
It's weird that neither Fowlers nor Robinsons Foundry recognise the number.
Couldn't you have your existing forks powder coated?