Personnally, I would sell a rare part that I BOUGHT. I would however say if you BUILT a piece, from nothing, with your own 2 hands, keep it, it's like your little love-child
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I'm just optomistic about my Z. I like to keep consistently upgrading, and I don't have a "final condition" that I can see the car in (one where I may regret selling a rare part).
Heck, I could see myself going carbon all around, then switching to luxury all around, then to race, etc. But I'm not attached to any particular part on the car. It's the memories, telling stories and talking car stuff with the people I care about that matters to me.
But i'm wierd so .....yeah