The average life spam of an antenna is 7-10 years depending on your location such as high industrial area, salt air, etc. Your 300 to 75 ohm matching transformer could have moisture in it do to age and weather cracking it. Another common problem is the coax cable getting moisture do to leaking connectors. Replacing your antenna may help depending on the ware on the antenna and of course upgrading to a larger system and getting it higher off the ground, with as much line of sight as possible.
The best system Winegard would recommend for you would be the HD8200U antenna along with an AP-8700 preamplifier and new RG6/U coax cable. Also try and install the new antenna at least 40-50 high above the ground. Also, with the way digital signal works we would recommend trying the antenna in several different horizontal positions to find the highest signal quality.
As for Philly channels having problems I suggest you call the TV stations and talk to their engineering department. They should be able to tell what their plans are.