Another way of looking at this is using the Prefix appropriate to the service you are (or not) getting from ATC.
Slow Oxy problem, decide descent in next 5 mins is a good scheme.
"Request Descend FL150 for minor tech problem"
"Maintain FL350, will check with next sector"
"Pan (x3) request descent" gets the message across
i.e. use the prefix to get the service you need, not according to the problem (which ATC can do diddly squat about anyway).
NoD