realoem lists that bolt for $22 or so, which usually means you can find it at dealer for about that cost or online for about 40% less.
Try bmaparts.com bavauto.com and search the 'incolnel' bolt thread...there was a big fight...many just use good grade bolts...not sure how good an idea that is, but in the scheme of things, could be worse!
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A recent set--NSFW audio: https://youtu.be/_dcxcZfD6dg
Mangofy your E46!