I don't care and neither should you!
there should be a fill plug on the side of the transmission case. its a bolt the size of a quarter.
If a 1988 Nissan Sentra is slow to accelerate when put in gear, the transmission might need to have the screen filter cleaned and the fluid drained and replaced. Older vehicles should have the transmission serviced after the vehicle reaches 100,000 miles and ever 100,000 miles after that.
when should the timing belt be changed on a 2007 Nissan sentra
NO. You should NEVER use any type of sealant on the transmission pan.
If your security sensor in your 2001 Nissan Sentra 2.0 is jarred or jammed you should have it replaced.
The 2003 Sentra has a chain not a belt and should in fact last you a lifetime.
The Nissan Sentra should not have any other heater installed due to fire hazards. The stock one is very good.