I used the rubber felpro ones when I redid my heads, and after 6 months or so now I can see a "ring" where oil has seeped past them. Also initially struggled to get them to seal. I plan on switching to the felpro cork, but am interested in the metal core ones as well.
Used FelPro cork gaskets with a little sealer on the cover side......2 years and no leaks.......used them on other vehicles for years without any problems........
"Life is a garden - dig it"...........
1968 F100 2wd - Rangoon Red - 360 w/T18 - power steering and brakes
1997 Honda CBR 900RR