Similar to Shytorque, I taught Gazelle & Astazou to REME Aircraft Technicians at Middle Wallop back in 1985. What has already been said is good info.
As the probe is in the return line from the oil pump (scavenge) to the oil cooler it will collect debris from the accessory gearbox, centrifugal compressor bearings, & the rear bearings.
Where the debris has come from can only be identified by someone who had been trained to know what to look for. The Army also had Experts at Middle Wallop and Detmold (long gone) who could decide what action needed to be taken.
Importantly it should be noted that if the engine Mag Probe is left out when the engine is running, the oil flow to the oil cooler is shut off and therefore no oil gets to the pressure pump to be passed around the system.
Hope this helps.
Steve