I have series 725 6' door, heavily used in California over 10 years. It's cheep all right, I noticed it when I adjusted the rollers.
Try them. I found this on the internet:
Croft Metals, Inc.
P.O. Box 826
McComb, Mississippi 39648
Please call us at 1-800-222-3195 during our business hours. When
you call select option 2 for customer service.
8:00am-12:00pm CST ILJA