Michael, Which kits are you considering? I've installed one and seen at least one other advertised, but they didn't seem to have much, if any, differences.
Note any kit AFAIK for the 100s requires machining the crank and some re-shaping of the rear engine plate. We did this for our BN2 and now the engine has excessive crankcase pressure and still leaks too much. Whether this can be attributed to the seal I can't say; I believe I would have checked the road draft tube for blockage but can't swear to it. A new thread just started re: drilling the rear main cap to drain the bearing. The kit we got--from BCS IIRC--recommended drilling but we didn't do it; the 100 crank is a known weak spot and compromising its support may not be advisable.
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A possibly better/safer solution would be to install a PCV kit. I'd pre-purchased a kit for my BJ8 but at overhaul my mechanic all but refused to install it. He said to stick with the PCV kit I had already, but he made some artful improvements. This car now uses a quart every 2,500 miles or so, which I can live with. I've acquired a well-engineered PCV kit for the BN2 and will be installing it as soon as I get some more round tuits.
precisionsportscar.com