I'd insist on the premium BRP cables if you don't already have them as that might make a difference. My cables are 6' longer than normal because of the way they're rigged thru the flotation tub and up thru swim platform, but they work fine. Also check out the
E-TEC Owners Forum if you haven't already seen it . . . there's a wealth of info available there, much like CSC!
What shape is your transom in! Any cracks coming out of corners of cutout or deflection if you step on lower unit? Is your inner liner original or has the boat been "restored" where someone removed much of the inner liner and the torsional stiffness it adds to the hull? My boat had a wood backing strip on the inside of the hull/deck joint to provide something for the tapping screws to bite into. Eventually the wood will get soft, and the threads on those tapping screws are so sharp that they cut fiberglass and don't hold well. Your best bet is probably to replace them with machine screws and nuts & washers on the inside.