Welcome back to Volvo ownership. For the money, the 850 is a great car. Very much a different beast compared to the 240!

The u-joint is a possibility, but from what you're posting about the dealer you bought it from, I smell something fishy. A new PS rack is essentially a precision piece of equipment. There should not be any "break-in" period where the pinion wears into the rack. Did they install a brand new rack and pump? That's not a small chunk of change to spend on a $3K car (and not an easy install either).

After doing all that turning how was the fluid level in the PS resevoir? Perhaps it had air in the system that needed worked out? This isn't the first time this forum has seen PS issues. Do some searching here for a similar problem (hopefully with a solution).

If you do take it back to the guys you bought it from, I doubt they will be keen to replace that u-joint after the hassle they went through to replace the rack. You may need to be extra persuasive to get some action.

Best of luck to you and the wife-to-be!

-Will
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850 / Mini