Whilst the car was up in the air, I took the opportunity to swap out the 1/2" UNF suspension nut on the lower rear arm. During our suspension set up session, the nut was re-used so many times. As it's a nyloc, the nylon ring must have been well beyond its best. 

Just noticed in the picture, a bit more of the powder coating coming off... I'll add it to next winter's jobs.