@adil39
You need an oil thinner at start-up. The pin is affected by build-up. Any good quality synthetic will do the trick if it can. Don't expect immediate improvements. It is a gradual process of a few oil changes. The synthetics you've been using are satisfactory but give it a shot.
I hope you can enjoy some NCPs while there. We never had those privileges in a forces family.
Edit: Do a read-up on sticking cold-start valves. It fits in-line if the rpm is truly above spec for outside op temps at cold-start.