The PO of my bike had the shocks replaced by the dealer,due to a leak,before I bought it. Still leaking when I bought the bike. 2 weeks ago,I tightened up the shrader valve,and it hasn't lost measureable pressure as of today.[good old "dealer maintained bike"] [I've also tightened up a few other bolts & nuts on this bike,on which the PO used as a selling point "dealer maintained"]
Buy a regular old valve core wrench. Take the shrader valve out,blow it clean lightly[or but a new one] put it back in ,and TIGHTEN it!
I had a '93 Classic that never lost any air pressure,on front or rear suspension

 

I'd start with the shraeder valve, replace the valve core itself. Then see if it works. If not, continue by using a spray bottle with light soapy water, and spray it on other fittings to locate leaks. Fix each as needed...