Reliance gas water heater 40 capicity, has a leak on the top

Anode might be leaking ... or water heater is rusted out:
Following link has troubleshoot walk-thru:
http://waterheatertimer.org/Leaking-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Following link has troubleshoot walk-thru:
http://waterheatertimer.org/troubleshoot-air-supply-for-gas-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

Unit is probably rusted out:
http://waterheatertimer.org/Leaking-water-heater.html

Reliance is AO Smith. I recommend the AO Smith line-up of water heater brands as best because air intake screen is located on bottom of unit and can be cleaned by homeowner without removing combustion parts, and because AO Smith posts service manuals.
http://waterheatertimer.org/How-to-install-gas-water-heater.html
http://hometips.me/Mar/WaterHeaterSerialNumberDecoder.pdf

Add a comment with more detail about leak.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

1) If water flow stops when tap is off, then Sound of water running: could be factory-installed heat trap inserts or nipples: These things cause noise.
http://waterheatertimer.org/Low-hot-water-pressure.html#trap
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html#heat-trap
http://waterheatertimer.org/How-to-troubleshoot-gas-water-heater.html

2) If sound of water continues when tap is off, then there is a broken pipe or leak somewhere in plumbing system.

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

You have to replace water heater.
But you can buy-time if leak is small by turning heater off except when you need hot water. This will give you 30-60 days to shop and find best heater.
http://waterheatertimer.org/Leaking-water-heater.html
http://waterheatertimer.org/How-to-install-gas-water-heater.html

To prevent tank from rusting in this manner, inspect and replace anode rod each 2-4 years, and keep water pressure below 80psi.
http://waterheatertimer.org/How-to-maintain-water-heater.html

If you need further help, I’m available over the phone at https://www.6ya.com/expert/gene_9f0ef4df2f9897e7

If cleaning doesn't work, try Amazon for the part. Around $40 with shipping and tax.

I wrote a page on leaking water heaters.
With a checklist.
It sounds like you've done quite a bit already.
The element can leak around the gasket.
The TP valve can leak where it screws into side of tank.
Otherwise a leak on side of tank sounds like the tank is rusted through and needs to be replaced.
http://waterheatertimer.org/Water-heater-leaking.html

You should turn off electricity and water to the tank, and open tub valve on hot side to relieve pressure so the tank will not rupture.
Then you can limp along with a failed water heater by turning the water and electricity on only when hot water is needed.
This will buy you time until a new heater is installed.
A typical electric water heater produces 21 gallons of hot water per hour.
A shower uses 6-9 gallon of hot water, so heater only needs to be turned on 20-30 minutes for a shower, more if the incoming water is very cold.

To economize with your next heater, you might read the following two pages:
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html
http://waterheatertimer.org/Replace-anode-rod.html

Your Reliance serial number shows your water heater was made in July 1994.

Except for the Marathon water heaters, and copper-tank water heaters, all tank-type water heaters are made of steel. That steel has an enamel coating which people call a glass liner.

So in that sense, there is a glass liner.
See a photo of the liner:
http://waterheatertimer.org/images/Enamel-coated-steel-290.jpg

Also inside the tank is an anode rode.
The anode is made to protect the steel tank.
Anode is made from lower noble metal than steel, so water reacts with the lower noble metal first.
The water eats away the anode rod instead of rusting the tank.
Once the anode rod is gone, the water begins rusting the tank.
The enamel coating does not protect the steel from rusting.
The tank rusts away and begins to leak.
http://www.thisoldhouse.com/toh/video/0,,20047047,00.html
http://waterheatertimer.org/Replace-anode-rod.html
http://waterheatertimer.org/9-ways-to-save-with-water-heater.html

i am not sure if you are talking about a shut off valve or the pressure relief valve. the relief valve should have a pipe from it going down the side of the water heater. if that is the leak the it can be replaced. there should be a little lever on top of it and some times by lifting it and letting a little water flow through, it will stop leaking.

If water is leaking from a pipe. then replace or repair the pipe or fitting. If the leak is coming from the unit itself, then replace the unit. Hope this helps.