408 , if you want to do more reading re. seastar there is a lot of info here;
https://www.thehulltruth.com/boating-forum/321796-seastar-steering-helm-pump-rebuild-pics-6.html
within that info a rebuilder outlines a ram test that I just ran on mine. it involves tipping the motor up and using the weight of the motor to test the ram seals, made sense to me . with the motor all up and turned a bit to one side I marked the ram w/ tape then you wait and see if the motor moves the ram over time indicating bypass in the ram ( or the helm if the wheel turns ) . I made sure to shove the motor the way it will fall to take out any play before marking the ram. on mine , overnight , w/ a good shove again I got about a 1/4" movement . the helm wheel did not move noticeably. the rebuilder said you should get 4 hours before the motor falls all to one side so mine seems to pass that test easily.
I am more confused than ever now that you have a new helm and still have play. on the one hand you and I seem to have similar symptoms and maybe correct. on the other hand andy's is much better . I guess I will get the parts together to make a simplified version of andy's bleeder. if I understand his system correctly it's just hoses from both bleed ports teed together back to the helm fill bottle . this is basically what I did before by transferring the fluid from the ram back to the helm bottle but with andy's system I can do it alone and watch the return fluid at the helm.
if you try the ram test please let us know the results.