I understand the intuitive wish to have the properly functioning drain holes, but these can be a nightmare to resurrect. I've never attempted on a Fiat, but I have on Scimitars and a Jag XJ, where they are notorious for causing corrosion in the inner wings.
There are two schools of thought on water leaks - and this was told to me by an engineer working on the Channel Tunnel construction back in the early 1990s, where they know a thing or two about keeping water out of things.
The first is, you assume there will be a leak, then engineer some system to allow the leaked water to drain. This is typically used on car windows. The second is, you don't worry about draining water away, because you use very high performance sealing technology to make sure no water can ever get in to start with.
You might think that second choice is naive wishful thinking, but in fact every single one of us uses it every day - sealed wet areas in our kitchens and bathrooms. Allegedly, it is also the approach taken on the British end of the tunnel. The French took the other approach.
The point is, from an engineering point of view both strategies are perfectly sound and viable, but obviously each has its drawbacks. You might think as I said that to get a 'perfect' seal is impossible, but as our flexing fibreglass shower trays daily demonstrate, to get a seal that is 'good enough' is perfectly viable.
As for drain tubes, you might take water away from the window, but then what do you do with it? The tube will never be perfectly dry; the water channel around the window will always be damp; debris can block it, etc etc, and then corrosion sets in not at the window but, as in the case with the Jags, in some other place that requires vastly more complex and expensive repair (in this case, replacing the entire front wings).
So, although ignoring the OE design and using sealant all around might be viewed as a bodge, and certainly isn't 'original', that doesn't mean that it is an inferior engineering solution.
Car window design like any other item is a product of its time, and of its mass production technology and costs. Sealant technology has come a long way since the Fiat assembly line of the 1950s, when these bodywork details were set in stone.
We readily accept windscreens bonded in place on a modern car using modern adhesives and sealants. Why not also on a classic Fiat?
