Here are the four sensors directly from rockauto. Not a WF discount code but here is a 5% code that I have
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NTK Part # 23141 NTK OE Type
Downstream Rear; 4; NTK is the OE Mfg
NTK Part # 23139 NTK OE Type
Upstream Front; 1; 4; NTK is the OE Mfg
NTK Part # 23142 NTK OE Type
Downstream Front; 3; 4; NTK is the OE Mfg
NTK Part # 23138 NTK OE Type
Upstream Rear; 2; 4; NTK is the OE Mfg
Personally I would replace them all if you believe the current ones to be Bosch, but that is your decision to make.