ProPress fittings leaking?

I have an oil fired boiler which is about three years old. The installer used Ridgid 'ProPress' copper fittings on most of the new water lines near the boiler. I noticed recently that many of these fittings are starting to develop a green stain where the copper tubing enters the fitting. Is this a sign of leakage? Should the fittings be replaced or recrimped?
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