i didnt ask about that, but i believe if the bearing fails, you need a new bearing cartridge. Also theres thrust bearings which fail from time to time and that would be an easy fix.

The restrictor advice is fine I suppose. I just know that everyone but Corky has recommended to me that for all BB turbos that smoke or don't have a built in restrictor you should use a .030 restrictor because ball bearing turbos don't need as much oil thus can handle the lower pressure.
http://www.atpturbo.com/Merchant2/me...egory_Code=OIL
ATP sells that restrictor solely for use in BB turbos.

Many journal bearing turbos smoke without a restrictor and many do not. Journal bearings rotate on a layer of oil thus the higher pressure created with a minimum restrictor size of .06 being used.

What Corky says about the restrictor size being no smaller than .110 could be fine. I see that only being necessary so that particles can pass through that oil line without plugging the restrictor itself. The smaller oil line might help enough as well. I run a -4 and see a max of 60 psi at high rpm of oil pressure at the turbo without a restrictor and using a .075 restrictor i saw 53 psi max. That gives you the idea of the pressure drop using a restrictor smaller than what Corky suggests.
So you have all kinds of options, i would suggest going and buying a pack of 1/8" aluminum pop rivets and inserting the rivet into your -4 AN fitting. It will smash smoothly inbetween the two fittings and not cause any damage to them. The hole measures out to ~.075 and will let you know if you need a restrictor or if you just have a blown seal or something. Worth the $2 if you have the time.
https://www.miataturbo.net/forums/sh...5&postcount=14
My tests on oil pressure the turbo with a -4 feed line.