No,the factory style valve seals can't just "blow off their seats" since they are held in place at the top of the valve.he drain holes in these heads are not straight thru but kind "L" shaped.It's easy for sludge,pieces of cork from valve cover gasket replacements,and the like to restrict these holes and cause a problem.Check the oil level after it has set overnight and note the level.Run the engine for a few minutes to warm it up,shut it down and check the oil quickly.If the level is down more than about a pint,you have a drain back issue.