ceslaw Any seal can leak or suck in as little as 20 miles. If the installed is worn out, or has edges where the seal needs to slide, it will cut the inner part and you will never see it. I don't know how many EDEL heads are assemblied per hour, but it is alot more than 2 sets.
use the white seals with the retainers on both the valve stem and the valve guide. Either comp or crane sales them. You can do this yourself. Valve spring compressor, Good little magnet,hammer, and piece of rope. Valve cover gaskets if you can't reuse the old one. Make sure you use the special lube or get it seperate for installation. This helps it slide right on. Push down until the seal is seated. Use plastic or a smooth piece of wood as to not rip, or spit the seal. Try and not push on the top where the valve stem is. The rope is pushed into the cylinder and the motor is cranked to hold the valve up. Take your time, about 2 hours start to finish. It's not a race. Listen to the little guy that sits on your shoulder
he knows when something is not right
Stop and call someone. Good luck
My number 732-254-3536 here almost all the time Rick L. I can talk you through it.