If this is the first timing belt change then by all means, change it. If not, then you have another 30K to go, assuming it was changed the first time at 70K. I would probably want to spread the costs out a little. I have read that the rear main seal is a 10 hour job. There may be a little labor savings with the timing belt and rear main seal but I can't imagine there would be any with the PNP switch. Also, most say you don't have to replace the water pump unless there is a problem. Apparently Volvo's water pumps are pretty stout. It used to be automatic with my Hondas to change the water pump with the timing belt.