I agree.
I think this might have been an issue during the production of the playfield. Not enough primer to "bite" into the wood. The sun may have dried the section up and as a result, it has split the paint creating the cracks in the playfield. not a common problem, but I've seen what appears to be this issue only a handful of times.
Trust me to get the one that does this. My reasonably hard playfield fixerup has now become a damn sight harder. This pinball has been teaching me one thing and that is patience!
