Hey Charlie and Gene Atl. Beach,
I've had simular problems with these parts and this is what I think the problem is. Unfortunately I did not take pics while I repaired this so the ones I'm showing are of the new replacement parts.
Gene Atl. Beach, the welds on my push rods also broke. SMB West sent me two new ones and I saw that the welds on the new parts had been beefed up a little. However I don't think that the parts failed because the welds were bad. I had the same problem as Charlie and the rods would get hung up in the shaft and would come down with a bang and a bang and a bang. The parts just aren't designed for that kind of force. So the question is why are they getting hung-up? Before I get to that, let me try to answer your question about the piston. You're right about it being welded. But you do not have to remove that part to remove the stainless steel piston. First, lift the top and support it with some 2X4s right at the top of the lifting bars.
Then lower the top just a little until the weight of the top is resting on those supports. Then pull out the pin that is holding the two bars together at the cross section. This may not come out easy so you may have to raise or lower the top so the pressure is taken off the pin. Once you get the pin out. the stainless steel piston will slide right out of the shaft.
Don't do this until you have the new parts, I don't think it's a good idea to have your top sitting on those 2X4s for to long.
So what caused them to break in the first place. Here is my theory. These stainless steel pistons slide up and down in the shafts as the tops raise and lower. Their job is to initiate the lifting of the top. They do this when they are bottomed-out in the sleeve. Once that stainless steel piston starts to slide out of the black sleeve it is no longer doing anything.
I think that the problem is when it is bottomed-out in the black sleeve it has all the weight sitting on the pivot point inside that sleeve. (This is the thing that Gene Atl. Beach referred to as the bolt that could not be removed). When all that pressure is put on two points it puts a slight dent there and causes a small burr that can cause the two parts to hang-up. But this is just the initial problem. The big hang-up is caused by the sharp edge of the stainless steel piston biting into the inner wall of the black sleeve. When they are assembled, they don't even ease or round off that edge. When I took mine apart I could see checks on the inside of the sleeve and knew that that was where it was getting hung up.
When I got my new parts I Really rounded off that leading edge and I filed in a almost half circle where the pivot point would make contact with the stainless steel piston. This was to spread the load a little more in hopes to prevent another burr from forming. As you can see, it is working well.
I also use to lubricate this part before I really understood what it was for and how it worked. It did seem to help but only for a short time. Even with the deep checks that are still in my sleeves, with the rounded edge on my new stainless steel pistons, they no longer hang-up and they do not need to be lubricated.
You can't see the checks in this photo, I couldn't get the light in the right spot but they are there.
This is not a big project. To take the pics that I used here, I had to pull apart this unit. It took me about 20 minutes to cut two 2X4s to 28 1/2", lift the top, put the 2X4s in place, pull the pin, take the pics, and put everything back together.
If anyone is having this problem with their electric top, I'm sure this will resolve it. Take a close look at those welds, if they aren't parallel with the stainless steel piston or look slightly bent, or you seem cracks in the weld, there is some abnormal pressure being put on these parts.
I hope this helps.