You can try Andrew/Prime Camera or Mr. Lim@Shaw Centre (#04-60). For Prime, they would normally charge about $80-$120 for such a job. For Mr Lim (IMO better skill), be prepared to pay more. Let him take a look at the camera and give you a quote.
I would say it is not cheap to service a rollei TLR in Singapore as only few could do a good job. However, if it is your favourite camera, paying 1-200 dollars to get it work perfectly might be worth it.