Originally Posted by
Graeme
The inconsistent height reductions suggests an air-spring leak but could still be a leaking valve in the valve block allowing pressure back into the main supply line, which is blocked by the exhaust valve. The valve blocks aren't particularly expensive especially compared with new air-springs or assemblies so in the absence of finding a leak in the air-spring, perhaps replace the valve block. If it doesn't cure the lowering then you have a spare front valve block which can be used in the rear, albeit with faster raising than usual due to the larger orifice in the front valve block than the rear catering for more front weight.