It appears from martyj pics that it is not happening on the inserts...so maybe the softer timber is the weakest point?

+1

I think there is large variance in the Stern playfields. Only an educated guess but Nino's TWD issue seems to be the clear-coat. Big dimples on top of inserts has to rule out the plywood as the primary cause. Not necessarily too thin - but definitely not hard enough (either the product or manufacturing conditions/curing time). Martyj's could well be softish plywood. Some owners seem to have no issues at all (or say they don't). Perhaps it comes down to the playfield & the day it's produced. I would not be happy with Nino's TWD playfield - it seems extreme to me. However, given all the reports of dimpling I'm bracing myself to expect severe dimpling in the 1st new Stern I buy. The big qn is whether to buy an additional playfield as a backup. Is it worth it come resale time?