yep you could use 10/30 but if it has much wear in it i would go higher on the weight, 10/40 maybe.
Let it run for a bit to get good and hot.
Just pay attention to the exhaust, if there is any bluish smoke coming out of it while running after it gets hot try a heavier weight oil.
Even though hour meters sometimes do not reflect the actual hours on a truck because it may have been changed at some point in it's past i'd be curious to know how many hours on showing on the one on your unit.
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