my experience with 600a and blocked capillaries has been primarily caused by the desicant in the filters disolving and getting caught up in the cappillary..

I have only found this on the spun copper type driers with the loose packed desicant and not the solid core type driers that you find on commercial gear.
I suspect that the driers and their ingredient are not comptible with hydrocarbon base refrigerants and just fall apart!!