I have the same problem (cracked brake cylinders) on my newly acquired C-150F. Serviceable used cylinders are difficult to find because most crack. That’s why I think Cleveland obsoleted the 30-63 series and why Cessna started putting Cleveland p/n 40-97A and 40-113 wheels on the 150H models and subsequent. The 40-97 series is a much better brake.
There are several vendors that sell replacement cylinders. The p/n for the 30-63 series brake cylinder is 061-01900. They are pricy (around $350 each) but MUCH cheaper than the Cleveland p/n 199-46 kit to covert to the 40-97/40-113 brake and wheel. Just Google for the 061-01900 number and you’ll find several vendors who sell new oem cylinders.
