Common problem with the repro mirrors for all first gen's.
I've heard that some have had luck by removing the mirror glass and tightening something(screws?) behind it...
Glass can be removed by soaking the whole unit overnight in mineral spirits to loosen the glue.
1969 Camaro SS, 350(NOM), M21, 12 Bolt Posi, 01B LOS Build
1977 Camaro, 350(LM1), M20, 10 Bolt Posi, Purchased New, (SOLD)