I sent my fuel injectors out to be cleaned and serviced by BUP (he did a great job, highly recommended). It was recommended to pull the fuel damper out of the fuel rails to clean it also and check for debris (flaky paint from old fool fuel 3's)

What I didn't know at the time was that Mercruiser does not sell the O-ring separately. You have to buy the 140 dollar dampener. It worked out where I was traveling so I couldn't measure the existing o-ring, and when I got back found a nick on one of the dampener o-rings. Lost a boating weekend. I have a new dampener coming in for next weekend, but I'm not happy about spending 280 dollars on basically just two o-rings.

So this week I measured the existing oring, and purchased a few sizes up and below, and found the exact size.

For those that also want to not pay 140 dollars a piece when all you need is new o-rings: I used soft Viton Fluoroelastomer O-rings, Size Dash -118. 7/8"(0.862") ID, 1 1 /16"(1.068") OD, 3/36" (0.103") width. McMaster Part Number: 1284N147
This is the oring for mercruiser part number: 8M0046753
This size o-ring is not common in many kits, as we tried to find one locally available last Saturday to salvage the weekend. The common sizes are to thick to work and will not fit in.
Compared to the OEM o-ring using calibrated Mitutoyo calipers.

I'm sure you can use a high temp silicone o-ring also. Hopefully this saves you all some money.
Below this oring is a flat spacer o-ring, it should never go bad. Though it measures .0625 at it's thickest, 0.9" ID, and 1.03" OD. It's a hard plastic, and again doesn't seal just spaces the O-ring out from the top of the dampener.
Below are the o-ring properties

Viton® temperature rating

Depending on the grade the working temperature range is considered to be -26°C to +205°/230°C (-15°F to +400°/440°F). But for short working periods it will take even higher temperatures.Chemical resistance/applications

Fluorocarbon elastomers are highly fluorinated carbon-based polymers used in applications to resist harsh chemical and ozone attack. Fluorocarbon O-rings should be considered for use in aircraft, automobile and other mechanical devices requiring maximum resistance to elevated temperatures and to many fluids. FPM (FKM, Viton®, Fluorel®, Technoflon, Dai-El) resist:

• mineral oils and greases,
• aliphatic,
• aromatic and also special chlorinated hydrocarbons,
• petrol,
• diesel fuels,
• silicone oils and greases
• high vacuum

Thanks for taking the time to post this info.

Yours is different - you have a dummy fuel pressure reg. late 2005 had the damper. The damper if it is rusty or crapped up a new one is needed. The damper is VERY important.

Yes working on all that as we speak