Fughedit. For what you'd have to spend on things like a vacuum pump, gages, brazing equipment. filling fittings and an online course/license so you could legally handle refrigerants, you could buy three or four brandy new window AC units.
Sometimes you just have to accept "disposable economy" things like that and resist the temptation to try and fix them yourself. The unit you have prolly cost you less than $15/year for the 15 years you've had it.
Jeff