How recent (and accurate) was the alignment?
Did the wandering tendency start afterward? My 940 was very "twitchy", requiring constant corrections till I checked the Toe (not rocket science) with a cheap Trammel Gauge from Harbor Freight (like an oversized, adjustable C-Clamp), and found 0° of Toe-In. (AFAIK, ther should always be some toe-in.)

I gave it about 1/3 turn of Toe-In on each tie rod, which resulted in about 2mm Toe-In measured at the widest part of the tire (B-to-b, Bentley 240 page 620-1), where the 240 spec is 2mm±1mm. (don't have 900 specs)

Steering is now much more stable. No tire wear effects noted.

I would get a 2nd opinion on the alignment. Maybe room for more Toe-In within specs?
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Bruce Young
'93 940-NA (current) — 240s (one V8) — 140s — 122s — since '63.