1991 B2200 Ticking
 

So I know that valve ticking is a well- known issue with the 88-early 90's B series trucks, I have a question in regards to the best oil in fighting this.
I recently picked up my B2200 up from a guy that was running Diesel grade 15W-40. I asked about this and got back, "I just personally prefer this." With this oil the truck would only tick for about 5 minutes on cold startup for about 5-10 minutes if it sat for more than 3 days. No tick if I started and ran regularly.
I asked around and was told to go back to 10W-30, which I changed to recently and the ticking came back with every cold startup. I ran about 16 oz. of Marvel's Mystery Oil and it still happens.
Should I go back to the 15W-40? I live in WA state and we're in the 50 degree mornings here heading into spring. I'm not a complete expert with oil, and I didn't have any issues with running 15W up until now, my main concern was wearing out the oil pump quicker as time went on.
Thoughts or suggestions?