Just let me add my sentiments.
He dutifully and patiently answered questions I posted, which to him, may have been redundant or those of someone just blurting out inquiries without truly thinking, and likely beneath his level of expertise. But when he did, it always struck me that, on this forum, I had the chance to get my posting answered by an ultimate authority and someone with vast knowledge of his field. That he took the time to answer me was special. One doesn't often get that opportunity.
I saw this notice and said out loud, "Oh, no!" RIP, Mr. Lehmann, you will be missed.