Re: 1999 40hp Johnson. Tilt n trim.
My shop allocation is 2.5 hours for a complete bench rebuild. This is from a raw system on bench through a fully renewed & tested unit ready to go 18-25 years. The flat rate repair rate on a freshwater unit is $250 including all hydraulic parts but not a new trim motor. The DIY cost is $90-200 in parts plus 3-4 hours time. $90 if you use 3rd party rebuild kits and $200 if you use OMC seal kit plus small parts. You should not need a new motor unless you are saltwater. The oem motor is one of best designs ever. Should go 30 years on a michigan lake.
The cap seals on this trim system are an incorrect use of radial shaft seal and U-cup. That is why you are leaking fluid after only one decade instead of two. Instead of using an OMC part you should go to a hydraulics shop and get a 16x24mm nitrile rod scraper (press fit with encased metal ring). This seal will last 15-30 years depending upon use and maintenance.
The rod wiper keeps water and debris out. In the lower section of cap is a shaft seal intended to keep oil in. E/J used the wrong seal here too. They used an inverted U-cup with the open end facing down. This is a low pressure seal. It is more important for the seal to be flexible around dings in shaft and to seal in both directions. The u-cup is easier to assemble and eliminates the need for an installation taper below piston shaft threads. However, it does not last as long or seal as well as a standard oring. The wiser choice when rebuilding is to gently file an installation taper and use an oring a quad-ring in Buna-70 material. These should be in stock at almost every hydraulics repair shop. You will need size #208.
You may also want to replace the poppets while you are working on system. The original OMC design does not use a sealing poppet. It depends upon the high pressure to drive the plastic poppet into the metal valve seat with enough force that the poppet will conform to surface. With age, this breaks the poppet down and leads to system leak down. You should use poppets in matched pairs - either the sealing design or the non-sealing design. Mixing poppet designs can lead to difficulty changing trim direction.
If there is any water in the oil - then you will want to replace all the ball valves (precision ball bearings). If your manual release is on the front, then you will want to replace the little oring on tip. it is size #008 in either a buna90 oring or a buna70 square ring.
