Not sure how clean battery terminals are going to help. The problem occurs when the battery is
removed.
Those other 'solutions' never worked for my two cameras. I see no way it has any connection to the type of SD card being used. That's just fantasy imho. Many people swap SD cards and buy new ones when the old one is full. I have an Optio S5n in the cupboard that never loses it's date, it's a 10 year old camera!
Thing is, the internal battery used is discharging faster than is should, they don't recharge it's likely just a button battery, like the battery on PC mainboards, if it's flat then the bios is reset and the date reverts to manufacturers default, but the computer still functions.
This is the battery for the Canon 350D's time/date.
And the Canon 40D
It's just a pity that Penatx don't make the time/date battery accessible so easily.
You can see the button battery on the right hand side in this shot of the Pentax K-r:
I think what we're experiencing here is a failure on the part of Pentax/Hoya/Ricoh to use decent internal clock batteries.