What happened to the Leica m6 bubbling?

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• Leica Noctilux-M 50mm f/0.95 ASPH
• Leica Elmar 90mm f4 3-element (III)
• Leica Summicron 50mm F2 V4
• Leica Tele-Elmarit 90mm f/2.8
• Leica 5cm f/1.5 Summarit

What happened to the Leica m6 bubbling?