Since you can smell the outlet, swap one out and see if it changes anything. If you're handy you shouldn't need an electrician.

Make sure to buy an AL / CU rated outlet just in case. You could have aluminum wiring since your place is 1969 - that can cause all sorts of issues. If your ground wire is coming from the same cable it should be copper colored. Also, if you're aluminum you might see some purple connectors if someone has mitigated it in the past.