Hi Levent,
On your eBay ad stating "all modifications" I notice that the upgraded DSP board with low pass filter has not been included. Certainly S/N 1230 did not include the new board.
This is not a negative comment on your sale but I have noticed this before on K3 sales. Is it possible that when an owner sends his K3 back to the factory and requests "all" hardware mods, Elecraft doesn't mention the DSP upgrade.
I found the mod listed on the following page
http://www.elecraft.com/order_form_parts.htm#K3%20PartsI see that the full board swap costs $110 and if only the low pass filter is desired the cost is $40.
73,
Mike K2MK