Praktica MTL5B stop-down lever stuck and wont budge

[prodirec]

Hi everyone. I just got a Praktica MTL 5 B and while the shutter and film advance work perfectly, the stop-down mechanism is jammed. The internal plate inside the mount that pushes the lens pin is stuck forward, meaning the lens is always stopped down and the light meter stays on constantly. The weirdest part is that the external black button is rock hard and stuck in the outward position, so I can't press it at all. It feels like the internal linkage is somehow jammed in the "on" position, physically blocking the external button. Has anyone dealt with this specific issue? I'm trying to figure out if this is a quick fix that I can solve by just taking off the bottom plate to clean old grease or free a spring, or if it requires a complex disassembly. I can still return the camera for a full refund, so I'd love to know if it's worth trying to fix it myself. Any advice is appreciated!