Tension Spring, Part # 195134
HelenAnn, according to the parts diagram for the Spotlight, there is a Snap Ring, Part # 195129, that holds the lamp together. I think this is what you are referring to that is "major pain to get back on."
There is also a Tension Spring, Part # 195134, that goes inside the lamp under the lens.
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Without this Tension Spring my lens fits very loosely and literally rattles around inside the Spotlight housing. It fits so loosely that the lens wants to fall out at any given opportunity.
Because it is a .pdf document, I can not copy and paste a full list of part numbers and their descriptions.
I have searched the internet extensively, and there is not one image of part # 195134 much less anyone that has one for sale.
What it would appear to be, is just a simple o-ring that is made of a soft flexible high temperature rubber or something similar that would compress easily when you install the lens.