i did the $12 replacment on my yukon you just stick it on the old, but it doesnt look as nice as the oe one. good enough for my third vehicle but when i had it to do over(on my bonnie) the new whole mirror was cheap enough, and they have plastic studs in there that get brittle anyway. it was definitely better just to replace the whole thing. i got some duplicolor paint matched paint and clear and you cant tell the difference now.
1998 Bonneville SSE
2007 Monte Carlo LT-KYB, Clarion, Polk audio, Kicker
1999 Yukon SLE-KYB, Air lift, Reese dual-cam, Tekonsha
1987 Firebird-355/th400-nothing stock