Well it's quite embarrassing  - but solved already. I had replaced most of the screws, nuts, etc - & near the end was waiting for the nylon nuts for the slings. When these arrived I put them on hand tight & intended to tighten them later - but never did. So yes it was simply the posts not being tightened down. Thanks heaps - silly mistake on my behalf - but you have saved me hours under the playfield or on the net. It plays perfectly now, zero problems with both kickers. Ta guys.