Cockatiel

I have a female cockatiel, she is a re-homer from my sister so I'm not sure of age, I've had her probably 11 years, I think my sistr had her two or three years prior (she got kitties so birdie had to go).  Last November (eight months ago) she developed a swelling in her rear, which our vet diagnosed as a blocked gland where oil is secreted for preening.  Warned us of the dangers of knocking the bird out, which we accepted. He drained it, she came out of the anesthetic fine, fluid wasn't cancerous.  The lump returned about four months later, growing slowly, had it drained again two weeks ago, vet says that there was 25ml of fluid! - and two weeks later the lump is back and almost as big as last time.  I'll talk to the vet again tomorrow, but I can't afford to be doing this every month - or more frequently!  

Any ideas?

[ireneo]

25 ml is equal to 1 tablespoon. That is quite a bit. Does the vet know why the gland gets blocked? Perhaps there's a way to insert a small drain in the opening to keep it stretched open for a bit until it stays open on its own. I wonder why there's the change just recently. Over the years things were draining fine. I see you posted this a few days ago. I hope you got some answers.