Healthy Head?
I usually reuse but I do the following: I clean the valve cover face very thoroughly and dry. Then I apply a light coat of high quality RTV to both faces of the gasket and immediately “glue” it in place on the cover. Set aside and let the head side of the gasket dry out thoroughly before installing. It’s worked well on the various slant sixes and Jeep 4.0 straight sixes I’ve run and both are famous for leaks. Also, and you may know this already, but go light on the torque of the valve cover bolts. Otherwise, the cover will distort and overly compress the gasket right under the bolt and leave weak areas between the bolts for leaks to form. If, when you remove the cover to do valve adjustment, some of the RTV or gasket cork stays behind, scrape off the residue and apply a light filler coat of RTV and you’ll be back in business. I also work on a Volvo C-303 for a friend of mine with the B-30 straight six. These engines are getting more and more rare and suffer from typical long straight six valve cover leakage. The gaskets are commanding over $100 on EBay if you can find them, so naturally I made sure I could reuse. I did the same RTV and dry-out procedure. No oil leaks, and it pops right off every time. As they say, your mileage may vary, but this has served me well for over 30 years of wrenching.