Try using Naptha rather than alcohol. It cleans better and evaporates faster. I use coleman lantern fuel, just a fancier can.
You should be able to operate the shutter with the back open by wedging the counter sensor with a tooth pick & advancing the counter to #1. Then you should at least see part of the operation.
I also think that if this were in a shop it would be beyond economical repair because if the flushing doesn't clear it up it wouldn't be worth the time to disassemble the shutter, or the cost to replace it.