M35b coolant leak at lower thermostat housing

[mattman]

I've finally traced a coolant link, it's occurring at my lower thermostat housing.

The gasket seems to have failed in multiple places, including around one of the bolts which has significant corrosion from contact with the coolant.

When I removed the bolt I saw little pools slowly form around the seam at top of the housing. Photos attached.

I was hoping I could replace this myself since the schematic seems straight forward...

http://www.marinedieseldirect.com/catalogs/catalog_group.php?owner=mdd&catalog=201021&model=M-25XPB%20M-35B%20M-40B&page_ident=201021-46&manufacturer=Universal&title=FRESH%20WATER%20CO OLING%20SYSTEM&size=800

But of course two of the bolts are completely inaccessible without removing the entire gear case assembly.

I'm looking for any advice on this repair and if it's doable with moderate skill. If it's just removing some hoses, bolts, removing old gasket material and replacing with the new ones (gearbox gasket and lower thermostat housing) then I'd try it myself.

If the gearbox assembly is more extensive I may just have to hire a mechanic. With which I'd happily take recommendations in Seattle.

Many thanks!

[mattman]

I spoke with a local mechanic and he recommended the following:

1. Drain the coolant and spray carb cleaner in the bolt hole and wait a few days for it to totally dry out
2. Replace the bolt and coat it with RTV blue silicone

He said hopefully once the thermostat is secured and the bolt hole is insulated the drip should stop.