F20 leaking after reassembly for cleaning

[fearoffours]

Hi. Using CPAP for less than 30 days
Took the mask apart for an overdue clean, Resmed F20.
Struggle to detach the two hard plastic bits from each other, but did it, gave it a good clean, left it to air dry. 
Came back this evening, went to bed, reassembled mask, but there is a steady, small leak somewhere- it feels like around the elbow valve that connects the tubing to the front of the mask.
Tried disassembling and reassembling, looking at videos- can't see that I'm doing anything wrong. Any tips?

[SarcasticDave94]

The cushion is probably not seated straight in the hole. Or not fully.

[Big Guy]

Make sure that the two pieces are properly aligned and securely fastened. I recall having F20 issues myself when it came ot disassembly and reassemby.