If it has been three months and you see your stats creeping up, AHI getting a little higher, it is definitely time to replace at least the mask cushion.
Altho most insurances allow for a new cushion every 30 days, new mask every 90 days and new headgear every 180 days, most will last longer. The problem w/replacing cushions every 30 days and mask every 90 days is that most local DME providers will not bother to keep mask parts in stock, they want to provide only the entire mask.
ResScan 3.10 - Resmed S8 ResLink & oximeter
ConTec CMS-50D+ oximeter - Philips EverFlo 5L Oxygen Concentrator
PR SystemOne BPAP Auto w/Bi-Flex & Humidifier - EncorePro 184.108.40.206