Euro indicator light gasket install - what's the trick?

I've seen comments in other posts about how installing the often removed front indicator light gaskets is a nontrivial task that takes time and patience because of the tight fit and uniqueness of each Dino body. Well I have new indicator light gaskets for my 71 Euro M-Series and wanted to know the best procedure for installing these before attempting this.

For example, does the light assembly need to be loosened or worse, removed first? Since they're attached to the body from behind, it would appear that if this approach is required (I suspect it is), then the inner fender panels and ventilation fans need to be removed to have much chance of getting even small hands to the backside of the light assembly. If removed, does the light assembly pull out thru the body opening or out the back through the inner fender/wheel well?

And since the car doesn't already have either of these gaskets installed, it doesn't seem obvious how they even go in; which side faces out (see attached photos), does the gasket's built in groove fit around the light assembly (I suspect so), etc.
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I got mine from MrFiat.com. I've acquired other trim rubber from them before (inner fender panel rubber). Claim is that it's made in Italy...experienced about 3-4wk lead time for both items.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=200391772990&ssPageName=ADME:X:AAQ:MOTORS:1123#ht_1329wt_913

 

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