Try putting a small, rolled up piece of soft foam rubber into the outdrive before putting the cvd/dogbone in (do both sides, dirt can work its way in past the washer on the non thrust bearing side). The foam rubber expands, seals out dust from the thrust bearing and ball diff, and doesn't interfere with the dogbone motion. I rebuilt my BX diff with carbide balls and thrust balls and doing this has helped it last two seasons.

I recommend changing the bearings and diff rings everytime you have it open. Visually inspecting those small bearings won't reveal if they are out of round or worn. Since both are cheap (especially the stock ball bearings, I admit I do reuse carbide bearings) it saves time of taking it back apart again in a few days.