2001 Toyota Camry valve cover gasket

I bought this car 3 yrs ago. Records showed valve cover replacement at 94,480 miles. At 98,719 miles the gasket was again replaced after a dealer (not the seller) reported oil leaking at the site. They speculated that the replacement had been improperly installed. At the 111,229 mile service, the mechanic again noted a leak at the VC gasket. Because it was under their service warranty, the dealer replaced the part at no charge. A different shop noted the need for a VC gasket at 116, 989. This time I elected not to replace the part. Now at each oil change mechanics note the leak. I notice a cloud of blus smoke when I start the car after it has sat for 3 days or longer. My question: what could possible cause such frequent failure of the VC gasket? Should I replace it and the oil pan gasket, which also leaks, even though the car does not need oil between change, nor does it leak on the garage floor.