Not sure the ins and outs of your system, but if loosing that much air, you should be able to easily find the leak with your ears. I've been running down leaks on our for a while. At first, my ride control valve bodies were leaking like sieves. My system mfr switched to a much better supplier, so I replaced mine with the upgraded valves (at around $350 ea). Big problem cured, but my compressors were still topping off the air tank approx every 12 hrs (110# on/145# off). That's not a big deal, unless it's 3AM. I soapy watered every fitting repeatedly. The final fix was the check valves (I also did a little more efficient replumbing for quicker fill rates, but I digress). I haven't heard my compressor go on (on their own) in over two weeks now. If working on it yourself, do not, do not, do not, use Teflon tape. Slow dry/soft setting pipe dope is the way to go with threaded fittings (Rectorseal 5, for example). Now put on your grubbies and crawl under that beast!
Big Okanagan on a big 4x4 Ram 5500.