My rally car man says its 'dry nitrogen' that goes into them but at what pressure is the question. Some of the suspension that the rally cars use have about 12-13 bar of pressure in them. But i dont know are they just 'gas shocks' or 'gas oil' like the hiperD are. I took two of mine apart the other day and there are nothing to bad in doing it and the shocks are quite simple to take apart just need to watch the order they come apart. The oil seals will need replacing and the oil was a bit crap looking so have to get some new oil. I dont know what to use yet. Its between fork oil for a bike or hydrolic oil and have to get some new rubber oil seals. But it has to the right type of rubber because the oil can it some types away. There are a local company who repair hydrolic rams and i should be able to get the seals from them. I starting to think these companys who rebuild shocks a realy taking the piss for what they could end up charging us. So if i just could find out what pressure to put into them they shold be 100% again.