Weird transistor failures

I have had a number of failures of simple transistor LED drives which I
really can't figure out why:

I am using a standard bc182 driven from 1 k directly from a PIC. The emitter
is grounded, the collector has two white leds (connected in parallel) , a
red LED in series and a 240 Ohm resistor. The drawn collecter current is
around 25mA.
The voltage is 12v dc and everything works perfectly for months
until...eventually (and not always) the transistor begins to leak such that
the LED's become just visible in the dark. The transistor will still turn on
fully but not fully off.

Anybody ?

Thanks
Tom


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