Well, your unconventional fix certainly shows ingenuity. If you value this car and its reliability, would it be unreasonable to have a welder tack a new metal plate in place? I can't imagine it costing a great deal.

Anyway, if you are concerned about the washer moving, but do not want to rivet, screw or weld it into place, can I suggest Devcon 2-ton epoxy between it and the firewall? Epoxy putty might work better, because it will not run or squeeze out of the joint.

I think you are crafting a temporary fix here, but I wish you luck.

The washer looks a lot better than a door hinge -- though the hinge would've gotten a laugh every time someone opened the hood :-)

Don't take this the wrong way.

But if the firewall on you car is so weak from rust that it won't hold the clutch cable....then what about the the rest of the car's structural ability to withstand a crash...to safely "crumple" as designed and disbuse the energy away from your legs, arms, head.... and save you from a major injury or death....as per Volvo's engineer's intent.

Only works on structurally Un-rusted uncompromised Volvo bodies.