The diffusion of the Italian terms for 'wine' from Etruscan

Back in April, Duane on Abnormal Interests had been pondering on the origin of the wanderwort "wine". (See Abnormal Interests: Friday Culture Word: *wyn(?), wine.) The topic is a rich universe unto itself and it's easy to lose train of thought with all the details. Although there are a myriad of reflexes for "wine" other than those I include below (eg. Kartvelian *γvino-, Hattic windu, etc.), I will restrict my focus to the reflexes relevant to the spread of this Wanderwort during the 2^nd and 1^st millennia BCE into the European world, more specifically how it might have spread to Italy:

Babylonian īnu
Ugaritic yanu (written yn)
Hittite wiyanas
Mycenaean wóinos (written wo-no)
Etruscan vina ~ vinum
Latin vīnum
Umbrian vinu

A standard view is monotonously common and yet not well proven, that Latin vīnum and Umbrian vinu were inherited via a Proto-Italic form ultimately from Proto-Indo-European *wóino-^[1]. Consequently, we're led to believe that Etruscan vinum, which was identical with the Latin, was simply borrowed. Since few IEists study Etruscan and since the academic standards among Etruscanists remains, shall we say, "much less strict" than that of IE studies, only a handful have enough gull or reason to question the received explanation.

Let's ask hard questions: Where does the final -m come from in Latin (n.b. final -s in the other reflexes attributed to Proto-Indo-European)? What exactly was the preform of this term in Proto-Italic that unproblematically accounts for both the Latin and Umbrian terms? Why would such an important ritual drink like "wine" be borrowed into Etruscan from Latin when everything else in the religious sphere (including the practice of hepatoscopy) appears to go in the reverse direction?

Is it not more likely that the Italic forms rather owe their existence to the Etruscan term? In favour of this opposing view is Carl Buck who refers to the un-Italic nature of the Umbrian term, concluding that it logically could only be borrowed from Latin, not inherited from Proto-Italic.^[2] From this we may infer a straight pathway into Italic languages from a foreign source: Etruscan vinum → Latin vinum → Umbrian vinu. While others have arbitrarily assigned the meaning of 'vineyard' to the Etruscan hapax vinac, I prefer to pay proper attention to the larger context from which it comes, the phrase vina-c restm-c, which more sensibly reads as 'both wine and lees'. While the final -m in the Italian wine words are annoyingly mysterious from a Latin perspective, from the perspective of Etruscan grammar, the use of -um to derive mass nouns is suggested elsewhere (eg. *meθil 'a gathering' → meθlum 'people').


NOTES
^[1] Mallory/Adams, The Oxford introduction to Proto-Indo-European and the Proto-Indo-European world (2006), p.164 where *wóinom is cited under Table 10.3 - Domesticated plants. Also read page 166 (see link): "The word for 'wine', *wóinom, is found in Lat vīnum, Alb verë, Grk oînos, Arm gini, and Anatolian (e.g. Hit wiyana-) and would appear to be old in Indo-European; it may derive from the verbal root *wei(hₓ)- 'twist', hence originally 'that of the vine' (see below)."
^[2] Buck, A grammar of Oscan and Umbrian: with a collection of inscriptions and a glossary, from Languages of classical antiquity, vol 5 (2005), page 21: "U. vinu 'vinum' (and O. Viínikiís 'Vinicius', if related) must be borrowed from vinum, if the latter is from *u̯eino-, earlier *u̯oino- (οῖνος). For the change of u̯oi to u̯ei is probably Latin only (U. uocu : Grk. ϝοῖκος ?), and even if it were Italic, we should expect then U. *venu (65)."


Relevant links:

Latin vīnum is from *wóinom as well as Gk oinos (?!)
PIE *wóinos 'wine' is based on *wih₁ḗn- 'vine' somehow