which Oasis do you have? I have an old Blizzard circa 1991,(basically the same as an Oasis) which had literally hundreds of dives on it in the early 90's at least a dozen beyond 150' and it breathed fine. All I did was have the IP increased when I moved to a warm water area. We still use this old reg quite frequently. It is going to the Caymans as a backup next month.
I have a newer Oasis, about 1999 which is just miserable at anything approaching 100'. It has been worked on by a tech at least 5 times and is better, but not very good. We use it as an absolute --everything else down--last ditch reg. This unit has driven me to USD ( sold and serviced by the same shop). I thought I had just gotten a bad one, but maybe not.