There shouldn't be a difference between hydraulic & solids. If there is a problem with the metallurgy, spring pressures, oil, break-in procedure, etc., you'll have problems with the cam & lifters with either one. I've used Amsoil synthetics in my hydraulic lifter engines before I switched to the Schubeck/Smith composite lifters with no issues. There are several synthetics that have plenty of zinc in them and it makes sence to find a brand that has a formula that includes enough zinc rather than playing "chemist".
http://www.amsoil.com/techservicesbu...t%20Tappet.pdf
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