Missing oxygen sensor heater relay

I discovered that my E36 323i does not have a relay at the oxygen sensor heater relay slot #3
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There are no fault codes registered, though. Is this indeed the correct location for that relay and what would the effect be if it's required but missing? Would only the agents stock them or can I buy elsewhere?

Highly doubtful that your car has an oxygen sensor - it was not required in our country at the time your car was first sold...

It has two sensors and IIRC they have four wires and are thus heated. There are no error codes registered and that made me wonder of #3 is indeed the correct location for the O2 sensor heater relay.