Leica Lens Rebates How often? When?

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I've been trying to put together a range of new/used 'M' lenses and I noticed that the 28mm f/2.8 Asph had a $300 rebate earlier in the year. I like this lens and an immediate purchase isn't required, but being new to all this I was interested in knowing what types of rebates Leica offers and on what products and what sort of timing. ie.. are most lens rebates at the beginning of the year? All lenses? some lenses?

Thanks in advance..