White smoke while starting up

I bought vehicle listed above it is a NV2500 with 60,000 miles on it several months ago. After a few weeks I went to check the codes and got a P0303 which indicated a misfire on cylinder three. I was advised to use Seafoam in the gas tank to try and resolve the issue and I did that but I also decided to change the spark plugs to see if that would fix the issue, I changed them all and a few of them had ash deposits. (http://thezenvan.com/images/IMG_0061.jpg). A little while after doing that I started to get white smoke on startup, at first I thought it was just a side effect of the Seafoam but it kept doing so for a few weeks so I decided to do a block test to make sure the head gasket was not the cause and the test showed it was not. I also changed the PCV valves to make sure they are not the cause. I also did a wet/dry compression test which came out fine. (https://i.imgur.com/OhZ4RXc.jpg) There were differences between the wet and dry results but they seemed to above minimum. There is oil being burnt because and I periodically need to add some. I tried putting Marvel Mystery Oil and doing an oil change too.

At this point I have no idea what is causing the issue, the warranty expired on it so I want to see if I can fix it myself. Any advice would be appreciated. Thanks