It is not just an old style pressed sheet metal valve cover with a cork gasket but rather is the upper half of the 2 piece cylinder head. It is precisely machined to fit the lower half of the head. These 2 pieces form the upper and lower bearing surface for the cams and contains oil passages. Properly installed the 2 will always seal unless there is warping or surface damage such as scratching present. It requires meticulous removal of the old sealant plus cleaning of the surfaces and surrounding areas before applying a VERY thin layer of the sealant (never enough to make a mess). It is not a job for the "hack" mechanic.

If the RTV sealed and does not break down in time.... no problem.
But....if the upper head ever needs to be removed again I cannot imagine how that would be done (if at all) without using a wedge or chisel which will surely damage the surfaces. The area that has been glued together with RTV is large and will not separate easily. Normally the upper head separates with minimal persuasion and no damage.