There's a known issue of negative cable connection coming loose after a few yrs, maybe it's worth a look!
https://static.nhtsa.gov/odi/tsbs/2015/SB-10057574-8899.pdf (TSB for Sonics sister car Cruze)
(13, 17, 22 dates)
BOT 402 75W85 Calcium Sulfonate+ZDDP, PAO+Synth Ester based synchromesh gear oils are gl4~gl5 low corrosion addpack is my choice across the pond and elsewhere available (from 22 quid).