IF your Cleveland Brake Master Cylinders are leaking, new O-Rings can be had for a very small around that would be less than 10% the cost of new Matco. IF you want to add dual brakes, yes the Matco could be used on the other side. Neighbor that had an RV-6A had Cleveland on one side and Matco on the other. I could not tell the difference in brake operation during taxi on either side.
Not sure what year but Van's changed to the Matco master cylinders because the cost of the Cleveland were a lot more money and in my option not any better than the lower cost Matco.
In my opinion, the Matco that Van now sells could be used to replace a damaged Cleveland that cannot be repaired.
I have the same Cleveland 10-30 that you reference in my RV-6. They are most likely three decades old and have had O-Rings replaced numerous times. I did post a PDF of the mil spec part numbers that Cleveland published along with the Cleveland part numbers in an old thread. The Mil Spec O-Ring part numbers are a fraction of the price of the Cleveland part numbers and are the same item. I can did up the document and post it again if a search does not find it.
Edit: Adding the PDF for 10-30 parts list and diagram.
