In California you can have assets transferred by way of an Affidavit of Small Estate. The Dept of Motor Vehicles (DMV) also has this form. You will need to state under oath that there is no person in a superior position to you to lay claim to his estate assets. You will also need to provide a certified copy of his death certificate. If your siblings make a claim against the DMV, then you will need to indemnify the DMV. Check your state's licensing department for a similar form. Otherwise, you will need to contact an attorney in your area to obtain advice particular to your situation. Since I only practice in California, I cannot tell you if Washington has the same law to effectuate transfers of small estates.
WA has a similar statute which allows estates valued at less than $100K and which do not include real property to be transferred by affidavit. This is still a complex enough process that you'd do better to have counsel. There is an attorney named Richard Wills in Seattle who does good probate work. He has a good website as well.
Hope this helps. Elizabeth Powell
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The problem is that with your father having died unmarried & without a Will, you & your sibs are his heirs & entitled to his estate --- not just you alone. Therefore, with the written consent of all of your sibs, you should be able to get the truck transferred into your name alone by going to a WA DoL office & submitting to them one of their Affidavits of Inheritance & paying the relevant fees. Without all of their consents, however, you have a problem, as you alone are not entitled either to all of the truck or to all of his property. In that situation, you're likely looking at having to open a probate for his estate, & that may not be worth it to you.
Richard Wills, WSBA 19720