I've checked at a couple of places and due to oil being a chemical, shipping it here is not going to happen. I've also checked with a few other folks and they confirmed that 50wt is not available in Korea.
One car shop I visited had 60wt, and someone suggested that 75wt or 90wt would be ok. I have no knowledge of oil wt's, so looking for advise from you guys here.
The Higher the number the Thicker the Oil.
I'd probably go with the 60 wt if that's all you can get.
Gear Lube is basically 90 wt oil, for reference.
I think why Ranger called for the Valvoline 20W50 Racing Oil is because of the varying conditions here in the States. Colder weather the lighter weight (20) would still flow and at Wamer Temps the 50 would still hold up.
The only way I'd really be concerned with the 60, if that's all you can get, is IF you get pretty cold weather over there where you'd be pulling the Trailer. If your Temps stay over 40-50* I'd say you'd be OK. Of course this just MY Opinion and your mileage may vary