On pg. 123 E I write "a short vowel following an r, l or n may be syncopated in an open syllable." But the last example *sakros > sakrs > *sakerr > sacer not conform to this formulation since the vowel following r in sakros is in a closed syllable. Of course, in sandhi the s would sometimes have been syllabified in the onset of the following word so r would potentially be in an open syllable, but that seems a pis aller. Another possibility is that s was already "weak" in this position at the time of this the syncope. Finally, are we absolutely certain that this syncope would not have applied in closed syllables? What happens to the medial V in an original sequence *VCRVCCV? I haven't come up with a certain case of this sequence yet.
Another point: the sonorant consonant only develops to e/iR if it is "stranded" in the nucleus after syncope. If the sonorant became a coda by syncope no epenthetic vowel develops, e.g. *porkelelos > porcellus 'piglet'.