Dripping toilet Even after changing washer

[ziucqea]

Hi guys. I live in an apartment which comes with Oli Expert Plus concealed cistern. About 10-15 minutes after flushing the toilet, water Would leak into the toilet. I’ve changed the seal washer but the problem persists. Here are some pics: 

 

I’m quite clueless… does anyone have a similar problem or experience what could be happening? Would really appreciate your help. 

Thank you in advance for your help!
Keith

[J-P]

I am assuming these wall units works the same way as regular flush.

Few tests to establish problem area. Shut off inlet valve after tank fills up if it leaks now then it is out let seal inside tank. If it stop then the inlet valve doesn’t close upon filling and it is overflowing.