Relay Valve Block

Hi

Had asked a question on testing the N75 valve which lives somewhere inside the relay valve block.  But now want to check the entire valve block.

Anyone know what I can test and how?

It's just that this is a kind of expensive thing to buy new 'just in case' and I'm not sure on the logic of buying secondhand when it is a sealed unit with plenty to go wrong inside. Some breakers do say 'tested' but wonder if they are really applying voltages across the relevant terminals and checking that the pneumatic ports are flowing (or not) as expected.

I have already done a vacuum test on all the lines into the relay block. Disconnected the 6 lines (one connector) then with access to the inside of the connector checked each line using a vacuum pump and gauge- all hold vacuum apart from the one which vents to the airbox this flows freely as I expected.

Have access to full VCDS, vacuum pump and gauge, digital multimeter etc.

Thanks