http://support.pentaximaging.com/node/1214 (USA) and
Note: This problem only affects the very early production batches and not all of them.We would like to express our heartfelt appreciation for your patronage of PENTAX products.
We deeply regret that the first shipment of our PENTAX K-5 digital SLR camera included some products with a stained image sensor — a problem which we believe was caused during manufacturing — causing them to occasionally produce images with spots which look something like water drops, and which users cannot remove with ordinary cleaning methods.
We sincerely apologize for any trouble and inconvenience this problem may have caused. We also promise to do all we can to achieve the highest level of quality control in the future, and eliminate any worries our customers might have about our products. We sincerely appreciate your kind understanding and cooperation regarding this issue.
It's best to contact CR Kennedy Directly for service, have proof of purchase (invoice) handy.
Also register your serial number at CRK.
If you purchased a grey import then get service via your supplier.
To check your sensor do the following:
1. Set your camera lens to manual focus
2. Set to Av mode and set f/22
3. Focus the lens to out of focus (usually at the short end)
4. Shoot at a clear sky or well lit plain light coloured surface (a plain door or blank wall)
5. Down load the image and check for moisture stains (they are quite different from dust, see the samples in the links above)