Any advice on proper torque for the plate to transom bolts?  Looks like they've been tractor tight in the past but I'm guessing they were over tightened at some point. Can't find a spec in the service manual. 

First,all bolts a graded.  Their torque capacity is determined by their thread size, grade and pitch. So for an example two 3/4 inch say fine thread bolt would have a different torque capacity if one is grade 8 and one grade 5.  Also metric ( and there are multiple metric pitches) are different than its us counterparts.  If they are us (inch) threaded either fine or course bolts they will most likely have 3 or 5 diagonal lines on their head.  I know I just ran around your question but I really did not. Tell me what size and grade bolt and I will give you the standard torque for that bolt. I have  charts in my engine manuals to cover them. If they are metric once again I have those too.  If I thought they were compromised what I would do is remove one and go to the nearest commercial bolt supply place.  My preference would be grade 8 over 5 always.  I would replace all of hardware with new including washers and stainless would be my choice, however they are not always available.  Tractor Supply as well as some hardware  stores otherwise many times you will have a commercial bolt supplier nearby.  Also sometimes West Marine can be a good choice to get bolts.  If you give me the bolt spec I will give you the torque spec. 

21 hours ago, fishnkamp said:

First,all bolts a graded.  Their torque capacity is determined by their thread size, grade and pitch. So for an example two 3/4 inch say fine thread bolt would have a different torque capacity if one is grade 8 and one grade 5.  Also metric ( and there are multiple metric pitches) are different than its us counterparts.  If they are us (inch) threaded either fine or course bolts they will most likely have 3 or 5 diagonal lines on their head.  I know I just ran around your question but I really did not. Tell me what size and grade bolt and I will give you the standard torque for that bolt. I have  charts in my engine manuals to cover them. If they are metric once again I have those too.  If I thought they were compromised what I would do is remove one and go to the nearest commercial bolt supply place.  My preference would be grade 8 over 5 always.  I would replace all of hardware with new including washers and stainless would be my choice, however they are not always available.  Tractor Supply as well as some hardware  stores otherwise many times you will have a commercial bolt supplier nearby.  Also sometimes West Marine can be a good choice to get bolts.  If you give me the bolt spec I will give you the torque spec. 

These are stamped 304 & DRA. I'm assuming the 304 indicates 304 ss and DRA is a manufacturer ID stamp. I can't find my thread pitch gauge. Seems like they're 1/2 13.  They could be m12 though.  I'll have to verify that one way or another. They used a bronze nylok I guess to prevent galling.  Aluminum washer in the splash well  I though thought that was odd.  There was some compression of the glass at the washers in the splashwell. Trying not to make that worse. I appreciate the help. I didn't think to check specs for the bolt size. 

Loctite® Red Threadlocker 262™ is a permanent, high strength, red threadlocker that is applied to fasteners up to 3/4" (20 mm) in size before assembly. 

A quick check in the internet concurs 304 ss.  They are grade 8 so they should torque to about 80 foot pounds. https://www.boltdepot.com/fastener-information/Bolts/US-Recommended-Torque.aspx    Here is a chart.

Remember what your application is. You can apply too much torque bolts that mount plates between materials that yield under the pressure. If your boat transum is fiberglass it has a very low modulus strength and will cold flow under high pressures.

Use  304 or 316 stainless steel lock nuts and tighten using a standard length wrench using your arm strength, without using a breaker bar or extension handle. Check the torque and it should be about 20-25 foot lbs. If the transum is metal you can torque close to the bolt strength.

As Catt mentioned a thread locking compound helps to insure the nut will not vibrant loose.

Use marine sealant to seal the bolt holes.

Tom