if the have a 1.3 or 1.4 we have been talking nonsense
I initially assumed a 1.1/1.2 as they have replaced the sump and it's fairly common for these to rust, it's also fairly common for third party plug to screw too far in and leak, the original poster hasn't been back after the first day, either they got the answer and fixed it or gone elsewhere
The plug is tapered, indeed.
I've put the sump back on the car and put the plug as always did, without ptfe tape. You are right @Pugglt Auld Jock, it's better safe than sorry. And there is no need for tape there. I just gave it a good tightening.