As I recall, it's a fairly straightforward fix.
There should be three tiny grub screws around the lens' facing ring. Remove those, then remove the facing ring. You should be able to unscrew the front group. Next, remove the middle element.
If this is a Pronto(r) shutter, remove the retaining ring. You usually have to rotate a small screw that has a portion of one side of the head removed. Turn it so the flat part is facing the retaining ring.
After removing the retaining ring, you should be able to remove the front of the shutter, which is the decorative plate, the shutter-speed selector ring and possibly one other piece.
Flush the slow-speed escapement with a mix of lighter fluid and graphite. Also, flush the self-timer mechanism. Allow the lighter fluid to evaporate. Make sure that you carefully clean the shutter blades. I usually remove the rear lens element and clean the backside of the shutter blades.
Once the lighter fluid is evaporated, blow out the housing to remove stray graphite particles. Reassemble the front shutter parts. Dry fire the camera. You might need to manually turn a gear in the film chamber to tension the shutter.
Make sure that all speeds work correctly. Reassemble the shutter.
Clean the lens helicals and relubricate. Recollimate the lens for infinity focus. Reassemble the front lens parts and tighten the grub screws. Not too tight -- "snug" tight.