Hydraulic ram seal fitment tips?

[HanSolo]

So I'm replacing the seals on my 709 backhoe attachment boom cylinder. Now I've done ram seals probably a dozen times and the o-ring I do last is the square one on the ram head that nests on top of the round o-ring. The rubber round o-ring is flexible and slides over the head no problem. But that orange square o-ring is made from a much less flexible material and does not stretch well at all. I've tried making the material more pliable by using a heat gun with good results but yesterday that o-ring stretched too much and wouldn't nest in the groove well. I tried putting the head with the loose o-ring in the freezer to contract but it still was loose. Carefully inserting into the bore, trying to fish the o-ring by the threads but the final push still burred the o-ring and I know it's not going to seal well. I've ordered another kit but what I really need to know... What trick do you guys use to get those particular square orange o-rings on the ram head?

 

[flyerdan]

I take it that the square ring is 9 and it has to fit in the groove of the piston 8.
I thought that it was sandwiched between the two O-rings, 12 and 7, but if it rides on them I've no idea.
Perhaps heating it in a can of hydraulic oil to about 250 and easing it on rather than stretching first might help to reduce deformation. I can see that if it's a hard plastic type of seal it won't easily return from any deformation.

While you're waiting for the kit, you might check out Youtube and see if anyone has posted a video on this, there seems to be a lot of that type on there.