The invention pertains to a composition based on a fluoroelastomer comprising nitrile or carboxylate-type cure sites and including a curing agent and a Br-containing marker having reactivity towards the said cure-sites, which can be cured so as to deliver cured parts maintaining chemically bound bromine atoms; this material, when submitted to wear/damage would hence release Br-containing contaminants, which can easily spotted via notably an on-line mass spectrometer, so as to monitor and anticipate critical failures of sealing materials based there upon.