1978 Ford F100 can 302, I changed my valve covers and they are leaking I used cork gaskets and aftermarket covers I didn't use gasket sealer not a mechanic just trying to get my Rig on the road. I was told to use gasgacinch but I can only find online any recommendations on doing this thanks guys

 

If cork is your choice then use this product Permatex High Tack gasket sealant between cover and cork only . If the cork gasket is already saturated with oil probably better to start with a new set. Don't over torque the valve cover bolts !! Gently retorque in 1 month if the bolts feel loose. 8-12 ft. lbs. is all that's required on these bolts. Here's a good read on the subject.

 

Where is it leaking? Back lower corners, or around the bolts? I would 1st off (flat edge check) those aftermarket valve covers. So how do you to that, you ask. Just take the valve cover off, flip it over and use a straight edge like a 6" steel ruler, but any solid metal item that has a flat thin edge can work. Place it on the underside of the valve cover where the bolt comes thru the cover, a little bit of your flat surface on each side of the hole, check each bolt hole area.

A lot of times people over torque/tighten the bolts and then bends the area and that you can get a leak easy enough. If you see a gap between the cover and your straight edge, you can apply a little pressure (rubber mallet?) and gently tap it back in place to have no gap. The X2 use some Permetex of "The Right Stuff" and use it on the gasket to valve cover underside using the bolts as a way to line the gasket and bolt holes up. Let it get good and tacky (as in stays in place) when turned over. Let is set overnight if you can.

Clean the head surface so no old gasket/RTV/dirt/rust/gunk is there, install the cover and torque it. You can rent a torque wrench from most auto parts houses with a tool loaner program. X2 yes then do a retorque a month or so down the road. You can re-rent/borrow the torque wrench and ck them right in the parking lot of the auto parts store. FYI that area will be hot.

In the pic below you can see the red straight line to represent the area to be checked. As far the the 2 bolt holes on the short side without a lot of straight room. A round item with a flat end (piece of pipe) and or a piece of strap metal bent in a curve can be used in those areas. Yes working on this rig is easy.

 

I've been using the same Fel Pro cork gaskets for years. On and off many times. The ones I have are a cork sandwich with metal in the middle. Never used sealant.

 

If you are having any cover distortion around the bolt holes, after straightening them, you may want to consider using some spreaders.