G'day Ross, the lack of a part number on the lhs suggests to me that it is aftermarket and of dubious quality. As I am sure you already know, springs should be replaced as pairs only. If not all 4, ie, rears as well .
hope you get it sorted soon
cheers always
Evelyn

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REMLR No 257
1966 FFT 114-087
1968 GS 171-953
1970 GS 178-313
1975 swb resto
1975 perkins 4128 donor
1973 swb
1972 lwb abused work truck
1978 ex mil 109 wreck 28-877
1982 stage1 diesel stn wgn
1985 110 V8 stn wgn
it's all good fun while they run!: