I have a 5 string Squier Classic Vibe Jazz bass and need some replacement tuners. The stock tuners are hard to tune and loose. Tightened everything up and still won't stay tuned very well. Can anything be done to the stock tuners to tighten the ratio? Can I buy a set of 4 and just one extra or do I have to buy 2 sets? Why did I buy a 5 string?