A/c Leak In 560sl

[sms]

I BOUGHT THIS CAR LAST YEAR KNOWING THAT THE A/C WAS NOT WORKING AND BELIEVED THAT IT WAS PROBABLY DUE TO A FAULTY COMPRESSOR. I'D LIKE TO CONFIRM THIS BEFORE REPLACING THE COMPRESSOR AND REFILLING WITH THE PRECIOUS R-12, BUT CAN'T TEST FOR LEAKS UNLESS THE SYSTEM HAS SOME CHARGE. CURRENTLY THERE IS NO FREON IN THE SYSTEM. I'D LIKE NOT TO USE R-12 FOR THE TEST! IS THERE SOME ALTERNATE THAT I CAN SAFELY USE FOR THE TEST THAT WILL NOT PREVENT ME FROM REFILLING WITH R-12 ONCE I FIND AND FIX THE LEAK(S)?

THANKS,

STEVE