I went to part https://www.partsbuilt.com/robo-parts/ site and see they have linear rods for R1+, C2, and R2 machines but there are 2 types (stainless steel and hard chrome). Which was the stock rod type and what is the advantage of the other? Just curious if anyone has had any experience or knowledge of these two types of linear rods. Would like to get some new ones for my R1, but would like to get the better of the two. Thanks.