I recently got this Minolta 7sii off ebay, it is in almost pristine condition inside and out
however, the aperture doesn't open up past f/5.6 manually
When I press down half-way on the shutter it opens up wide, then closes down to f/16 before releasing the shutter, this happens on all f/stops as well, so it's essentially stuck on f/16 when I press the shutter release

Here's a video I made explaining the issue
https://files.catbox.moe/y3xti7.mp4

The shutter speeds all work fine, including Bulb mode, and the leaf shutter behind the aperture also works flawlessly, so it's only the aperture giving me this weird issue
I've heard ther blades tend to get sticky after being left in storage, but they have no trouble opening up wide when I press down on the shutter, so is it really that?

Any help on what I could do, or what it could be would be great