Finally after much procrastination I've at last hammered out a provisional model of Etruscan verbs. My pdf, originally focused on Etruscan declension, now includes what I hope is a coherent and natural model of Etruscan conjugation. Given the available literature, I fear that I'm the only one that dwells on these little details. So please review it in the Lingua Files section. This is to be, as always, regarded as an ever-evolving work in progress for discussion.
One will notice that while amace '(he) has been' is often parsed as am-ace and called a "perfect", I elect to interpret this more elaborately as three morphemes marking both aspect and tense: am-ac-e = be-PERF-PAST. As such, I specifically call this form the perfective past which contrasts with the perfective present-future seen in eniaca 'shall remain' (see Pyrgi Tablets) which is then similarly composed of the verb root en 'to remain', the perfective -ac- and the present-future marker -a.
My model has the benefit of finally making sense of uncomposed Lemnian -ai which marks the verbs recorded on the Lemnos Stele. Surely these too then are imperfect pasts. I don't know of a competing model that can address these various facts as well. It seems too that treating -in(-) as a mood marker works best with a grammatical structure of tense, aspect and mood. So I've settled on calling this a mediopassive which contrasts with the default active mood. It's interesting too that both Greek and Latin, two languages having notable influence on Etruscan, had this same mood. "A product of areal influence or just accidental?" I wonder.