I'm using a 2.5kohm resistor between the base and the ULN2803 outputs.
You need pull ups to the +ve and a resistor in series with the base.
So then i'd have the the emitter to 18v, a 2k5 from base to the ULN, a 4k7 from the emitter to base, and another 4k7 from the emitter to the ULN?
Loose the 2K5 and yes.
A PNP transistor is effectively a diode from base to emitter ( base cathode ) and pulling too much current from the base WILL destroy the transistor, Short the base to ground and the transistor WILL explode or shut down the power supply, in either case the transistor is toast. ALL PNP transistors need some method of current limiting (A resistor) in the base circuit. If it was an NPN directly pulling the base down, likely the NPN is toast as well.Bob
Also, when not connecting anything to the transistor except for 12v on the emitter
Then you are missunderstand what I was saying. Can you draw what you are doing.