These 100mm 2.8 Planars are rare as hens teeth. Around 1980 I had purchased an XL system, which proved to be a disaster. However, I salvaged my investment by saving the lenses for a MF view camera and trading the rest of it to a local XL swap-meet "dealer". A guy came into my local camera store in 1985 (I being a well-connected customer) to sell them his XL stuff, mainly two bodies, two 100mm 2,8 Planars and misc accessories. They were not interested, however they referred me to him. His story was that he was a retired professional photographer. The XL system had been purchased new in 1962 for a state contract job doing aerial photography of the right of way and construction progress for an interstate freeway. He paid over $5,000 in 1962 money and had never used the stuff again. He wanted to sell everything at once to avoid the hassle of parting it out, and he wanted around $4,000 (A price which was ridiculous in 1982). I think I offered him $350 for one Planar, but we never got past his demand to sell all or nothing. I explained to him that there was no market for XL stuff because the bodies were a total failure, and if I had to buy everything, I'd have to resell it piecemeal, so I'd only offer 50% of used retail value, or around $1,000 tops. He might have been interested in an extended negotiation, but I was not. I thanked him for his time, turned and left his shop. I periodically wonder what became of those lenses. Probably, he died, and the widow tossed it all in the garbage.