By suggesting an interconnected series of soundlaws for the outcome of Proto-Indo-European (PIE) falling e-vowel diphthongs in final syllables in Proto-Germanic (PG) and in the individual Germanic languages, viz. PIE *-ei̯(C)# > PG *-ai(C)#, PIE *-ēi̯(C)# > PG *-ei(C)#, PIE *-eu̯(C)# > PG *-au(C)#, and PIE *-ēu̯(C)# > PG *-eu(C)#, this article renders superfluous the old, prevalent assumption of competing o-grade allomorphs in some of the oblique cases of the PIE i- and u-stems. Consequently, the i-stem gen.sg. is reconstructed only as PIE *-ei̯s (not as †-oi̯s in addition), the u-stem gen.sg. only as *-eu̯s (not as †-ou̯s), the u-stem loc.sg. only as *-ēu̯ (not as †-ōu̯), the u-stem voc.sg. only as *-eu̯ (not as †-ou̯), etc.