my brothers car was doing something strange.

when driving on a motorway in 5th after a while the oil light on the dash would start flashing and there was a beeping noise.

he slowed down and moved into the slow lane and went into 4th.

this stopped it. but it came back after a while of driving in 4th.
pulled over and turned the engine off.

let it cool down for 5 minutes and drove off again. and it was ok.

done the same thing for a while.
and also done it when he was in neutral sometimes around town, but not when in gear.

the way it was happening it was as if it was monitering the gearbox not the engine.

he changed the gearbox oil (he was planning on this any way) and it seams to have pretty much sorted it. it stopped doing it on the motorway.
and now a week later its stopped coming on at all.

he checked his engine oil level often and it was fine.

any ideas what could be going on?