I need to replace my rear callipers too. I've had my existing ones cleaned out and lubricated before, but they've seized up again.
At higher speeds I get a continuous high-pitched squeal from the back end, although strangely only when I'm accellerating.
I'm going to have mine replaced with mk3 ones as the cleaning trick is clearly a short-term fix.
When I bought the car the same rear calliper had created so much heat that the wheel bearing had started oozing grease! Lovelly! A bit of a swine to clean off your wheels too!
Its a J-reg, 1991 registered, so I guess I'm looking for new late-model mk3 callipers, pads and discs yeah??