When buying oils or grease it should be shown that these lubricants are OK for copper materials like in gearbox bushes or synchro rings . Most of the modern recipes should be allright today. In doubt do the copper strip corrosion test as described in this PDF:
Link:
https://www.panamlubricants.com/wp-content/uploads/2016/11/Copper-Corrosivity-ASTM-D130.pdf
Vic
Link:
https://www.panamlubricants.com/wp-content/uploads/2016/11/Copper-Corrosivity-ASTM-D130.pdf
Vic