𐌱

ambivalent letter MB? not really. The only incidence is resolved unambiguously at that time

𐍃𐍄𐌹𐌱𐌽𐌰 stιbna Stimme!! στόμα
𐍃𐍄𐌹𐌱𐌽𐌰 stιbona stephona steven™

ambivalent letter BH⇨F? not really: The rare cases can be explained with later sound shifts:
𐍃𐍅𐌹𐌱𐌻𐍃 Schwefel

There is one ever important word though which links Gothic to Persian:
𐌳𐌰𐌲𐍃 𐌰𐍆𐌰𐍂𐍃𐌰𐌱𐌱𐌰𐍄𐌴 dags afarsabbate Tags after Sambet-(Tag) day after saturday: Sunday