I know the "Ubi caritas" has been moved to the Offertory on Holy Thursday, but we still do it at the Foot Washing, and "Dextera Domini" at the Offertory, under the rubric " ...vel alius cantus aptus." We replace the chant (I know that's very modern of me) with the Duruflé setting, which is too short for the liturgical action, Duruflé possibly not intending the motet to serve in that way. It's also possible that he knew the rubric referring to "Ubi caritas" in force at the time of his composing -- "The following must never be omitted. It is begun towards the end of the Feet-washing, omitting if necessary some of the preceding pieces." -- in which case Duruflé would assume we'd sung one or more of the other chants provided for the washing. In any case, we sing only the Duruflé, our choir, clergy and congregation expecting that. I have altered Duruflé's score to repeat from meas. 8 to the second bar of page four, adding the second verse "Simul ergo", which makes the piece about the right length of time for washing 12-24 feet :) If anyone would like it, let me know. I'm pretty sure copyright laws would prohibit me from posting the inner pages here. If you hate the idea, "C'est la vie!"