Best stuff to affix a plastic lens to a metal case....?

[gooseEL34]

Have a 90s Guitar effect box that has a 3 digit, 7 led display mounted on PCB.
Restoring it and removed the metal case.  There is a rectangular hole in the metal case, into which
sits a red plastic piece with a "lip" on the edges.   

What goop would be good to affix the edge of the red plastic lense to the metal case?  The original material seems to be a black gooey substance...

Thanks
Tim

http://www.franknitsch.com/ART/pics/sgx_mid.jpg

is the image.  The rectangular lens goes in from the backside and has a flange/lip that keeps it from coming right through the hole.   I need a substance to apply to that edge so that the lens will not drop into the unit and down (as the LED counters don't actually push up against the lens, keeping it in the rectangular hole:

Thanks
Tim

[CatalinaWOW]

Faced with this I would use hot glue.  The standard stuff from craft stores.  Just a tiny bit, carefully applied.  All the usual precautions for any adhesive (clean, dry surfaces and so on). 

You want something that has high viscosity during application so that you can keep it off of the viewing (and viewable) surfaces.  You want something that stays flexible so that the vastly different temperature coefficient of the plastic and metal can be accommodated without damaging the plastic or ripping the joint apart.  (Whatever you use you will have to pay attention to this.  Don't try for a lap joint with a very thin glue line or nothing will work.  Just think about how things will need to move and set the glue location to accommodate it.)   There are a variety of RTVs that would work, but curing time is long, cleanup is messy and so on.  If you are careful enough they will work fine.  A clear one would be ideal for cosmetic reasons. 

There are other choices but I don't have them at my fingertips, and they won't be found in every lab or carried by many suppliers.

[Ian.M]

Be careful what adhesive you use. The wrong solvent can craze or cloud many types of clear plastic, for some distance away from the glue line.   Hotglue is solvent free and most silicones are fairly low risk, though its advisable to check compatibility with the manufacturer.

[ovnr]

Hot glue is always a bit iffy IMO. I'd go for a decent RTV silicone.

[jwm_]

E6000 is my goto glue nowadays. It is slightly compliant so doesn't break down when things thermally expand at different rates.

[gfiber]

I use BRON's Killer Red double sided tape on camera concealments even use it outside in normal Pacific Northwest weather year round and have yet to have the tape let loose.
http://www.brontapes.com/product/bt-3854-original-killer-red/

[gooseEL34]

Thanks all!!!