This is the best possible CPU I could find that *MIGHT* work on that laptop. http://ark.intel.com/products/40479/Intel-Core2-Duo-Processor-T6400-(2M-Cache-2_00-GHz-800-MHz-FSB)
I do not take responsibility should the processor fail to work. My findings are based on the fact that the laptop has had that processor available in variations of the same model. Its been said in the posts above that some r510s have the CPU soldered onto the mainboard, making replacement impossible. You do this at your own risk.