The TC3/4 shock bodies (blue) have no groove for the bobbin to snap into. The offroad bodies (gray) have a groove for the flat "square" piece to snap into. Its a different setup. The TC3/4 bodies hold the bobbin in place with friction, and thats it. The 8 points on the bobbin force against the walls of the shock body to keep it in place. There is a definite "snap" heard when you install the offroad shock parts, but the TC3/4 parts just press into place. It is possible for the adonization to wear enough on the inside of the shock to make it hard to hold the bobbin in place... not through wear of the piston... seeing as it doesnt go down that far, but through consistent and often rebuilds. (i have an old TC3 set that are no longer blue on the inside... but mostly silver!) This however would be harder to happen (age) than say just forcing the bobbin in place and deforming the 8 points of the bobbin and making it harder for it to stay into place. If the bobbin "snaps" at the top of the shock as you insert it, then it is deforming the tips of the bobbin. Try inserting it at angles till it is in place with no "snap" at the top of the shock. Are you using the old skool AE shock tool to build your shocks? I dont know why AE doesnt include that simple tool anymore... it works great.
- DaveW