Correct, the rears are very different. I have similarly not seen any full metal ones. Just the all-plastic or metal+plastic as you show in the pic. BTW for that pic - odd that they show the cable routed through that hole in the metal; it does not go through there at all.

What I have found is that for the rear, there is no real way I can see to strengthen it to make it last longer. Vs. on the fronts, I typically use zip ties and epoxy to solidify things. As it is in the fronts, the tension in the cable causes some off-axis bending of the plastic, eventually leading to failure. The zip ties keep things better aligned, so not off axis, and the epoxy keeps it in place and strengthens it.

In the rear, there are little springs there that are supposed to provide some compliance, so I do not think epoxy will help. And they look to be on-axis, so no need for zip ties.

In general, since the pic there appears to be a slider clip + cable set, I'll say that if your broken regulator is an OE one (Brose, I believe was the OES for my car's regulators; or of course a genuine BMW one), it may be worth rebuilding. But anything else, I'd replace with new. Even a cheap new China brand one, since it will be newer junk vs. older junk.

And of course you'll need a new window clip to hold that slider clip to the window itself. Different parts for front vs. rear. Front needs 2, rear needs 1. Rear costs 6x what the front does.

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2001 X5 3.0i, 203k miles, AT, owned since 2014