starting to restore an AGS 38 receiver and see a 5GL. Should this be replaced along with the usual capacitors? Just wondering if it would be likely to fail after 50 some years.

Not exactly certain what a "5GL" is but if it is a selenium rectifier stack, it might prevent some minor future inconvenience if you replaced it with a silicon rectifier module at the same time as you replace the caps. Selenium stacks have a fairly graceful failure mode- they open up rather than shorting out- but are said to produce an offensive, possibly toxic, gas when they fail. The silicon bridge will have a lower forward voltage drop than a selenium stack so a series dropping resistor may be desirable to prevent B+ from rising to an excessive level.

My personal experience with selenium rectifiers is that if they aren't abused (by overloads due to shorted capacitors, etc.) they will last indefinitely.
However, I know that many radio repair folks have the opposite opinion of them and replace them as a matter of course when recapping.

I have an AGS AM/FM receiver from about 1962. Good quality Japanese radios, breaking into North American markets with a better product, IMO. American General Trading Co.

Your unit probably has a fuse to protect the transformer? I would be inclined to bypass the selenium rectifier anyway, but only because of what CV said. Reputation for flareups.

http://www.radiomuseum.org/r/american_g_communication_receiver_ag.html