Rock shaft on 1210

[tree grower]

The links on my 1210 (2300 hrs) drop from their own weight when it is very cold. This has only happened in the past couple years, so I assume the problem is an O ring on the rockshaft piston. The picture in the repair manual (fig 273) doesn't show an O ring. There is a seal ring --does that serve the same purpose?? Is it likely that the problem is a defective part in the valve assembly? I would like to know what defect I am likely to encounter before tearing things apart--if possible.