SL960 Flash (1st Gen) O-rings

[vintageair]

True to my handle, I've just acquired a fully functional 1st gen SL960. (SL96001) This version has only one trigger sensor and a single cover compression screw (no clamps).
Before I drown it, I decided to examine the back cover seals. They appear to be made of a soft translucent material, possibly silicone. The perimeter seal is circular and rectangular in cross section. It and the perimeter seal surface look and feel fine. On the other hand, the single center cover screw shaft seal needs attention. The plastic bore is slightly scored from the accumulated corrosion that was on the chrome plated shaft. The shaft and bore are almost exactly 8mm in diameter (tight fit even after cleaning). The seal slot is exactly 5mm in diameter and 2.5mm wide. I am assuming that a replacement should be an o-ring (not a custom shape) under slight compression when installed. The metric o-ring size I am looking at is: OD 8.32mm; ID 4.76; CS 1.78. (Viton and Nitrile 70 are avail in this size at one vendor I looked at) Because of the bore scoring, I think I need a very compliant material like Silicone with a low durometer like 50. (I want feedback on this).
The switch shaft (no magnet) appears to be tight and corrosion free (likely stainless), so I am reluctant to disturb it.

->For the shaft seal, what material should I choose? (vendor suggestions welcome)
->Given the bore and slot sizes I've got, What size o-ring?
->Should I try to smooth out the bore? If so how?

I've attached pictures of the flash, screw shaft, shaft seal, seal bore and perimeter seal.

I have nothing but good things to say about the SeaLife staff that I have talked to about this, but since this version is SO old (almost 2 decades), there is little information available to them. And almost no modern SL9xx strobe parts are applicable to this unit.

Thanks in advance, -Vintageair

 

[vintageair]

In case others have a similar o-ring design problem...
I am posting my design progress.
The center shaft seal was unavailable from SeaLife. The large perimeter cover seal is available in a kit since it is similar to later models of this strobe which use a hinge and cover clamp.
To size the shaft seal, I decided to use the on-line Parker o-ring calculator.
For the center shaft I used a 4.8mm ID x 1.9mm CS JIS standard size P5 o-ring in Nitrile Dura 70
See design notes below.
I did smooth out some of the rough parts of the plastic bore with a dremel pointed polishing felt tip, using toothpaste as the polishing media. The dremel was used sparingly to avoid overheating the plastic.
After replacing the shaft seal, I tested in a 5 gallon bucket of water.
The large (86mm ID x 3mm CS) outer case o-ring or rectangular profile seal leaked.
The new shaft seal did not leak.
I replaced the outer o-ring and seal with the available SeaLife seal kit, Part Number: SL9605
Upon re-testing in the bucket with new perimeter seals, the housing did not leak.

Actual dive testing will come soon.

Notes on shaft O-ring sizing

Used Parker O-ring calculator. Click on link below:
inPHorm

Letting the calculator select oring size:
Start with "Gland Design", then
"Radial Dynamic" , then
"Select O-ring Design Group", then
"Design O-ring for Me". then
"Select Application", then
"Male Reciprocating Seal", then
Enter the Dimensions and Tolerances (if known),
then select "Calculate".

Inputs (Actual Measurements):
Groove Diameter: 4.9mm
Groove Width: 2.5mm
Rod Diameter: 8.0mm
Bore Diameter: 8.01mm (Estimated)

Calculator Results were:
ID: 4.8mm +/- 0.13
CS: 1.94mm +/- 0.08

I chose JIS standard size P5.
4.8 x 1.9mm.
Used Buna-N (Nitrile) Dura 70
with light Silicone Lub and
If that doesn't hold up, I will use
P5 Viton 70 o-ring which is more resistant to abrasion.