So I tapped the lower tube up into the upper tube cap today. I did learn one thing that may help someone else. I didn't have a 16mm deep socket, so rather than go buy one just for this, I was able to use a 5/8" spark plug socket. Easy to find and does the job well.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles

The outside diameter of the Sockets made by different Companies varies; especially on deep Sockets. The cheapie deep Socktes tend to have a lagter OD (and are often shorter) than the better quality ones. So you need to use what ever fits.
5/8" is a common Spark Plug Socket so if someone has a gasser they are likely to have one.

I only posted the 16mm because that is what I actually used to do the Job. I cant remember if I just grabbed it first Socket I thought would fit or took some time trying out different ones to see which one fit the best.

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84 300D, 82 Volvo 244Gl Diesel

All done. Preliminary drive showed no leaks. Will continue testing.

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Mike Frederick
1986 300SDL, 240K+ miles
1985 300D KaliKar, 270K+ miles