Will this high slide work with the orignal L-398?
Yes, it fits perfectly! The picture is an optical illusion, of sorts. Great fit-must have!
Yes. it's the proper high slide for the l-398. Mike
Mine fit somewhat loosely and overexposes about 1/2-2/3 ev.
I'm using it only with the current Sekonic L398 but I suspect it will perform identically with the older models too.
The plate causes exactly 5 stop reduction in the light reaching the sensor, so if the difference between the "default" arrow indicator and the "H" (high) arrow indicator is 5 stops it should work as expected.
I cannot tell if its dimensions are the same for the older L398 since I have never worked with the older one.