I'm having some issues with the 4HP22EH auto transmission in my '86 635. Its the electronically controlled type.

I'd like to understand my options for sourcing a replacement should I need to go down that path. Will any 4HP22EH transmission from an E28 535i, or E34 or E32 fit the E24 without any mods? Or were there variances between vehicle models and/or years of manufacture?