Hello John. I expect that it has probably got a leak on the air bags & the compressor has got weak as you say & is cutting out due to overheating.I would remove the compressor & check its' operation & if found to be faulty or weak,replace it ,but also check the air bags carefully,preferably by removing them & inflating them & using soapy water to find any leaks,as it is usually very difficult to find any leaks with them in place.It is also possible to get water in the compressor via the intake filter in behind the rear light cluster(offside i think),but i doubt that you have that problem,as i think the compressors usually seize when they get moisture through them. Hope this Helps,Regards Andrew