Help please. Co2 problem or maybe ok.

Hey guys new to the world of home brew. Bought a kegorator and some used postmix kegs. At 1st the pressure. On the co2 regulator was dropping cause I had bad reconditioned kegs. Now that I found the problem and I'm pretty sure I fixed them. The regulator is still going down a bit.
On the regulator I have to manual valves to shut the lines of to the kegs. So what is happening is I set the gauge to 40 psi and within an hour it drops to 38. But once I close the line of to the bottle the pressure rises. Then I open the manual valve and it goes back to where it was(38)(originally set 40). So I adjust it back up to 40psi. I've thrown spray and wipe all over the top and can't see any more leaks.

Is the dropping of pressure normal. Or do I still have a leak. Please help.

Forgot to say co2 bottle is outside the fridge. And the manual valves are shut of valves.

I'm confused. Are you saying your CO2 cylinder side gauge is dropping, or keg side? I assume it's the cylinder reading, as 40 psi seems high to carbonate at. 40 psi also seems low for cylinder side, should be way higher. How old is the tank? When was it last filled? I usually recommend not worrying about the remaining pressure in the cylinder, as they're filled by weight. The mass of the empty cylinder should be marked on the side,
I would weigh it and subtract the difference to see how much CO2 you have left. It doesn't sound like you have a leak anymore, and if memory serves when I helped my friend (I'm a CAMRA advocate) the pressure drops keg side as the CO2 rushes in and attempts to equalize with what's in the tank.
Hope this helps, get back to us.

The keg side and the co2 bottle is full. The home brew shop told me that to carb between 280kpa to 300pka which is close to 40psi.

40psi is way to high. Some of us force carb at 30psi for a day or two, but then drop it to prevent it from over-carbing. If all else fails, use 12psi for a 35-40 degree beer. Use a chart to get exactly what you want, but don't use 40psi.

Here is a carbonation chart for temp and PSI to get the volume of CO2 desired.

Ok, a little lower than 12psi when the temp is low. But the chart does not lie. Note that 40psi isn't even ON the chart.

A 2lb variance could be caused by expansion of the lines, 40lb is a lot and they weren't exactly designed for that.

Well I did a blonde beer. I'll have to ring around and ask all my local suppliers. That's what the shop told me to do. What do the no.s in the chart mean

Those are the volumes of CO2. Just treat them as relative carbonation levels. The higher the numbers, the more bubbly the beer. There are style charts that will tell you what you should use. But also feel free to adjust to your own taste. I myself prefer less carbonated styles.