I have a 1977 mgb with an alloy head. It is a stock style which has shims under the two middle rocker shaft pedestals. The head appears to be leaking oil between it and the block on the manifold side and I was wondering if those shims could be causing the ends of the head to be pulling up. Is there a need for those shims as it is a pain to mount the shaft as it has to bend up in the middle.