My DT1 needs some tuning and looks like seal replacement is a start. 

I ended up using what was in the shop ... a few pieces of 1/4" stainless steel and cut a few block off plates, then fit them w/1/8" rubber as you suggested.   Have large tray of air gun parts, so used quick connector and welded it to spark plug lower.  Removed crush washer and 
added an o-ring.  Worked out great.  There are MANY ways to do it, but this one works fine for me. 

Data: 
*leaks on mag side crank seal.  pressure test loses pressure at a rate ~2 psi in about 20 seconds. Test were run as you suggested at 5psi.
*loses vacuum also about the same rate.  

Parts for the job.  1 missing is on intake now. 

seal looks like may an original. had chip in lip. 


chip in lip. after review of video, it appears the leak is right at this location. 


video of leak; I should have used something to brace the camera. lots movement.