Preventative maintenance items SHOULD NOT be required performed by a certified Yamaha technician. The recommendation is that it be performed by your dealer. If you are a DIY owner and have full knowledge of the maintenance requirements and procedures, using OEM parts and lubricants. You should keep purchased parts receipts, oil, gear lube, drain plug gaskets, filters, plugs and anodes. I'm an advocate of oil sampling for two reasons, I have documents showing the sampling dates and I have a record of oil sample trends in the event that the engine is developing internal mechanical issues. If you are a DIY owner I would recommend owning an OEM engine service repair manual. This will outline the recommended procedures of all maintenance items. Many engines have different ways of draining ,filling lubricates, filter changes, prop shaft inspections greasing and torquing. If you use the OEM factory service manual you are doing all maintenance items as per manufactures recommendations and sometimes better than the hourly flat rate technician that has the certification. Take your time and don't cut corners. Document everything you do in a engine log book. If you don't know how to perform an item don't do it until you know how to do it correctly. If you don't have the right tool get it. If you don't know how tight something should be find out. I enjoy working on the boat and engine. The maintenance for me is part of boating. The more maintenance I perform the more I know about the engine and it's operation. This gives me more confidence that if a failure were to occur I may be able to safely get back to port. Talk to your local Yamaha dealer about doing your own maintenance. Purchase your parts from them. If a warranty issue arises and the dealer knows you have done the required preventative maintenance items I don't think you will have an issue. My Opinion !