Gruen 490SS Mainspring Problem Advice Needed

[CoastsidePockets]

Recently, I serviced a Gruen 490SS automatic but ran into a mainspring issue. Apparently, this movement uses an older style automatic mainspring. Rather than a bridle, a short piece of mainspring is wound into the barrel with a metal tab at the end facing toward the arbor and a regular manual mainspring is inserted inside this. I suppose it still needs braking grease, but I am not sure. this is the first time I have run into this type of automatic spring setup. Well, I broke this small piece. Any ideas of whether I can replace this whole system with a more modern bridle mainspring or possibly fabricate this smaller piece of mainspring out of the end of another mainspring? Below is a photo of the original spring, a new spring I bought, and the small piece and its broken end tab, all seem to be old. Loved working on this movement and very bummed I was so clumsy and didn't think this through before taking it apart. I have about 20 working watches now (and many non-working projects mainly due to my poor judgement). I am learning (and relearning, unfortunately) not to go into an unknown situation without doing some research and careful thinking. I seem to need to relearn this lesson too often. Anyway, I would appreciate any advice. First time using this forum and a graduate of Mark's first 3 courses and loving every minute of this most rewarding hobby.

[RichardHarris123]

Hello and welcome from Leeds, England.

Yes, you can use a modern mainspring. Breaking grease, protects the barrel from excessive wear. 

[AndyGSi]

Welcome to the forum.

Here's a good site that in your case shows the original along with the modern alternative.

https://www.emmywatch.com/db/movement/gruen--490ss/

[CoastsidePockets]

Thank you both. One clarification please: Of the two mainsprings listed above, which one is the modern bridled version? That is, which one should I buy? Again, thanks for your efforts. This is an invaluable resource.

[AndyGSi]

The GR3257X is the new generic spring.

The X on the end signifies it's an Automatic Spring.