I just came back from Busan and wanted to share info that T money top up service is available at a few locations in Nampodong.
1.) The GS25 convenient store at Nampodong underground shopping (link to subway) just outside the basement entrance to LOTTE Department store. Immediately next to this GS25 is Tony Molly.
2.) The GS25 near to Jagalchi fish Market building. If you are walking straight from Jagalchi Market towards BIFF Square direction. You will see it on your left before crossing the road.
Not all GS25 store has add value service for T money. Look out if there is money orange outside the store.