Feb 12, 2013 update, No Customs agent at Rio Sereno - on Costa Rica side
Just an update from my experience yesterday from Panama to Costa Rica at Rio Sereno border crossing. The ride from Volcan to Rio Sereno is awesome, with great scenery, plenty of twisting curves with elevation/descending curves. Highly recommended.
At the Costa Rica side of the border, the migration office is staffed for your passport stamp, but this is low season, I was told, and the CR customs/aduana office for importing my moto is not currently staffed.
I had previously imported my moto in to CR last week and then exited at Paso Canoas for a few days in Panama. My CR import paperwork was "suspended" at that time.
At Rio Sereno, since I had my insurance and suspended import document, the migration officer called down to Paso Canoas and informed customs. The customs agent from Paso Canoas took a truck ride up to Rio Sereno and an hour and a half later I had a new inport document to enter Costa Rica. Cost a few tips but was worth not having to re-enter Panama and riding down to Paso Canoas.
A suggestion, prior to riding to Rio Serento/Sambito crossing, call ahead to find out if the customs office is open. otherwise, enjoy the ride from Rio Serento to Volcan. Paved great motoring ride, flowers, scenery, more fincas and haciendas then I could count.