Sadly, yes, crap design/materials is the issue and yet noone seems willing to make a more solid replacement, probably due to the fact it'd be an arse to machine and to complicated to cast in metal :-/
I'd go TDC first, then do the long hop mod if your feeling confident, as the TDC will straighten out the shot, the long hop will add range and accuracy at range
I did mine using an M4 nut and bolt, a tension spring (to stop the bolt un-winding).
Measure the exact centre of the outter barrel, and the point that is over the centre of the hop window of the barrel. Make sure you do the measuring bit a good couple of times as accuracy hear is paramount ( I f**ked up my first attempt by hold ing the outer one way and the hop chamber I was using to find lengths from the other, only realising when it came to re-assembly
I then drilled and tapped for an M4 bolt, you must make sure you get this absalutely spot on upright or it makes the next part a bit of a ball ache and it looks horrible on the finished job though I dowt it affects the out-come to drasticaly so long as its not to far out, then take the bolt with the spring and nut assembled together and fit into the threaded hole, I then glued the nut into place to increase the effective length of the thread depth.
Re-assemble the hop/barrel and fit it in the outer after backing of the adjuster bolt until the hop chamber slides past easily.
Before re-fitting the bolt/reciever adjust the bolt to the point you can just see the hop rubber coming into the barrel opening, dont forget to push the bb holder up while you do this

, enough to hold the bb with-out it falling right through. Mark the bolt head so you know where your start point is, re-assemble your gun and go try it out..... adjust bolt to suit your ammo..... job done