I am confused all of your problems seem to be regarding condensation (the sweating on the tank and the "sweaty pipe"). Those are signs of humidity in the air and cold incoming water temperatures. What you are asking is how to mechanically repair the toilet (which you have given no sign there are problems).
In many places warmer weather is also more humid weather and with the water in the tank close to the same temperature year round there is a greater chance for condensation.
To you actual question, if there is nothing wrong with the porcelain, then yes you can replace all the valves seals, bolt and mechanicals. They make things called toilet rebuild kits that will contain all of the toilet internal mechanicals (bolts flappers, valves, and so on) and of course you will need a new wax seal, supply line, and shut off valve to replace everything.
If it truly is a condensation issues not of that will help. If the supply lines are sweating your best bet is to go in the basement and insulate then with standard pipe insulation. For the tank they make toilet anti-condensation liner kits (basically internal insulation), but I haven't heard great things about them. They also make anti-sweat valves, that mix in a little hot water (you would need a hot connection) to bring the temperature of the tank above the condensation point.
You should also check to make sure the toilet flapper is not leaking. If the toilet tank is constantly leaking into the bowl and refilling it will sweat more as it will stay cooler longer.
If you decided to get a new toilet as a result of this look into getting one with low flush volume and an insulated tank.
If the toilet is in a bathroom with a shower that gets used the extra humidity from the shower might not be helpful. Consider taking shorter or cooler showers, running the exhaust fans in the bathroom for a period of time after a shower (my parents have a timer on the exhaust fans), and possibly using a squeegee to get water off the shower walls.
