Wood bifold top guide

A handy person from Illinois says:
I've scoured the internet trying to figure out the design of this top guide. The bifold doors will not stay in the guide rail no matter the adjustment at the bottom and I am now wondering if I'm missing a set of guide wheels and/or springs. The house was built in the early 1980s and there are no markings. The rail ID is approximately 5/8 inches. Any help would be appreciated. We have 5 sets to repair.
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Paul from SWISCO responded:

Many thanks for your correspondence. We have a wood bi-fold top spring-loaded guide pin with a 3/8" top guide cap, our 23-122. You will need to drill a hole to accommodate the spring housing base. Let us know your thoughts.

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