I should be no problem. However as with all synthetic oils they have excellent cleaning properties in them and if you have a small leak that has be plugged be engine oil deposits, the synthetic oil will flush away the deposits and the leak will start up again.
That only if you have not been changing your oil on a regular basis. I had a 92 Caravan that I switched to synthetic oil after 120,000 KM and had no problems with leaks at all.
Without a doubt synthetic oil provides greater protection under extreme conditions over conventional oil. Such as when its -20F and you need to start the engine. Or idlingin gridlock traffic when its 110F outside. Some even say synthetic oil cleans the engine better, although this is mainly a function of the detergent additive in the oil and not the base oil itself.
If you change the oil yourself, go ahead and use synthetic, the cost is minimal (it costs more to fill up just 1/3rd of a tank of gas than the cost of synthetic over conventional). If you are paying someone to change your oil, it gets more expensive (as they mark up the oil too). If you use a quality oil filter (such as Nissan OEM) you can also safely extend your oil change intervals to 7000 miles or more.