$300 - $350 is about the standard asking price for good looking Magnums around here. If it does not have the clear-side fuel tank, I'd subtract about $50. If it has cracks anywhere in the fuel tank, I'd subtract $100 or more from that number. 038 screw-cap fuel tanks are getting VERY hard to come by. The magnesium fuel tanks crack and break very easily, and I would not use one on a work saw.
Factory triple port mufflers are nice and add value, as well as wrap handlebars. Check the oiler function and gears if you can get a look. Those oilers are kind of complicated, but will throw ALOT of oil when in good shape. Upper A/V mounts can crack and loosen things up. Most of the 038's through here have some kind of wiring issues. It is very simple, but annoying when it won't shut off without the choke. If the switch shaft is "loose" the only way to fix it is a new spring for the switch-shaft. I have tried for hours to re-bend them, and the best option is just to replace the spring. Fuel vents are frequently missing on those. Don't let a little fuel leak sour a deal, as it may just be a fuel line or vent. I recently lost out on a trade thinking my fuel tank was leaking, when it fact it was just the fuel line grommet. Good luck. 038's are good saws. In the right hands, Magnums can be made to run with MS-460's in the power department.