well i got a reply from sterns warranty division, here is a paste of what they said i will give it a few days before i reply but i'm thinking of asking them to sell me a nos playfield so i can have it clear coated and hopefully they will sell it at a discounted rate.

 Hi Ben,
We are currently looking into the cause of this planking you're describing and showing pictures of.  Please let me know what I could do to correct this issue for you.
 
Regards,
Patrick

had a good look at all of mine last night & they are no way near as bad as yours
ask for a free PF