I made an aluminum one a decade back and have had no problem with it. Note that in measuring the stock cover as installed, you may find that the seal opening is not centered on the crank nose in either plane. This means the crank nose orbits around inside the seal, likely not extending its sealing life. When I made mine, I centered the seal opening. And if you're going to this much trouble, I suggest making an adjustable timing pointer holder.
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