The sealant on my relay board in the engine compartment is getting old and crumbling on the underside...what is used to reseal it?

There is a thread on RoadGlue on this. I have seen the material and is an perfect match. It flows pretty freely. Be sure to plug the relay sockets.
Relay board sealant thread

Looks like the model cast is the way to go. Thanks for the info.

Model Cast is a polyurethane...aren't polyurethanes hygroscopic (they absorb moisture?) I would think thats the wrong material to use for this purpose, regardless of how it looks.

I didn't see that it is polyurethane. Where did you get that? It is a 2 component casting material. The finished product looks exactly like the original. I am sure it is different but looking at it it looks real nice. Glenn has used it a number of times without problems.

we use 3-m "windo- weld" urethane. It is 08609

So Jeff, I was going to jump in & tell him to contact you for what you showed me that you use on them - so what was that stuff, just tar again?

IIRC you're right about the urethanes, which is why it holds moisture in the body cavities where similar products were used on our 914s - like at the sail/fender junctures!

So George's suggestion may not be much better for attracting moisture, than the Model Cast.

IMHO - if not original spec bituminous tar - then if anything, a flexible liquid rubber or sealant type product may be the best alternative, if it dries solid & won't be too runny to stay in the tray bottom during "casting" of it.

...A type of potting material(not soil)
wurth maybe??

looks like tar

I just did a quick google search and found these:

http://www.glenmarc.com/VAGABOND%20MODEL-CAST_CAT_2010.pdf

Any corrosion effects of moisture absorption to the circuitry/conenctions over time would be concealed under the coating. Same problem as the original bituminous coating.

What the Vagabond tech sheet is refering to is each component's sensitivity to moisture before they're mixed together. This is common with two-component polyurethane casting materials. Optimally you'd evacuate the mixture before casting to remove entrapped air and moisture.

Andys

That is how I read it. Once it is cured, it is pretty hard. The worst thing to use would be RTV. This out gasses corrosive gas. It also absorbs moisture.