Losing oil... time for heavier weight?

[JJorgensen52]

I switched my '69 307 to Mobil1 synthetic, 10w30, the last time I changed the oil. (Not here to discuss the use of synthetics, I have my reasons and will be sticking with the Mobil1).

that said, the truck has been loosing a lot of oil, almost exclusively during highway driving. Like, about a quart for every 125 miles. It's got no trace of leaks and it isn't smoking like I would expect.

So my question is, assuming I have worn valve seals (compression is even at least, seems fine but will be checking it next weekend), will going to a heavier oil help reduce the rate of oil consumption? What weight do you normally run?

I'm looking at either a 10W-40 or 15W-50 at this point.