Welcome and I have no idea what your mechanic means by "welding 2 steel arms together". Maybe he means the 2 tabs sticking out on the inner damper plate??
And welding to the outter frame plate???
This can only be a temporary solution at best and the cost to get at the automatic flex damper is at least 10-12 shop hours and beyond.
You can cross your fingers and go used on a damper. EBay or try Pelican used parts forum.
We have a good used parts member-
www.944ecology.com.
Here is a PET diagram.
This is a new damper
GL
John_AZ
1988 924S + 1987 924S