Leaking toilet waste pipe joint

Hi all
There has been a small leak at the joint of my toilet waste pipe (where the pipe connection to the pipe inside the wall). I have put in some plumbers mate (the gray thing in the photo) around it and it usually solved the problem for a few month and then it appeared again. Any suggestions appreciated. I’m not a diy person at all, so do I have to call out a plumber to sort this permanently, ie, dismantle the joint and change the washer ? Many thanks!

I have marked the place where leak occurs

The toilet has to be removed and either a new seal fitted ,or a new pan connector . if you dont wish to tackle the job ,then call in a plumber.

Chances are the fins on the flexi connector are not doing their job anymore, that and the flexi connector seems very level (little or no fall), therefore water may be pooling at that point and then working its way back past. Time to get the connector out and have a looksee.