I've had similar issues and ended up fixing by cleaning the contacts in the backbox. I've also had to pay a tech locally and he found that one of my relay stacks was broken and proceeded to make it right then and there. That game had been messed with previously while yours looks cherry so I'm guessing it's in need of cleaning/adjusting. I know it's a no-no but I use an emery board. Safe bet is a business card.