That 0.67" is almost exactly the Outside Diameter of a 3/8" pipe nipple. I read where an OP (might've been Cloud Driver) posted that Velvac uses a hydraulic press to compress that spring down to get the retainer clip on.
Wait! I think I've got it:
1. Select a Pipe Nipple to fit inside the broken Velvac part. Ream out the Velvac side or file/grind the nipple to fit inside.
2. This nipple must be long enough to extend past the Spring in its uncompressed state. THREAD the nipple far enough to reach where the retainer was.
3. Grind/file the Velvac part to where a nut and washer on the nipple will compress the spring to were it was when originally assembled.
4. Epoxy this "long" nipple (with extended threads) into the broken Velvac piece.
5. Assemble Arm, Spring, etc. with Washer and Nut.
6. Draw spring into compression and till the washer/nut shoulder down onto the dressed-down Velvac part.
7. Add RED Assembly Grade LocTite to the last few threads as the nut approaches bottom.
8. Saw off the part of the nipple used to compress the spring, flush with the nut. Might even be able to get that little black trim piece back in place.
NOTE: Using Pipe Nipple should accommodate those with powered mirrors. Otherwise, a piece of 5/8" threaded rod or a cut-off bolt with long enough thread. Maybe even a 1/2" bolt or rod.
Opinions?
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB