i dont know if its the cold weather that is affecting it or not, but when i try to shift into 3rd gear while the car is in motion, i need to use force / more power than i used to to get it in there while my clutch is pressed all the way.

its only doing this on 3rd, nothing else

is something going out? the tranny has over 200k on it

 

Is it grinding or clashing syncros? if its grinding third and its hard to engage then I would say that the third gear syncros are shot. If it isn't grinded then I would look at the shift linkages and change the transmission fluid to Honda genuine fluid. I read a service recall for the 92-93 Acura Integra YS1 5-speed transmission and the service recall said if the transaxle is making alot of noises in neutral and in gear and is difficult to engage certain gears, to change the fluid to honda genuine instead of using regular motor oil like most people reccomend when changing transmission fluid. Usually if I come across a transmission that grinds and clashes gears, I try using GM syncro-mesh or Redline manual transmisson fluid and it at least will make it easier to shift if not cure the whole problem. Check the linkage especially if you just installed a short shifter, it could help to get new shift linkage bushings

 

it doesnt grind at all, no noise. it just takes alot more force to put it in 3rd than it normally will.

i changed the fluid with honda genunie MTF 1/2 yr ago, about 15k miles on it

 

Having a tranny with over 200K is a miracle within itself if its stock and has never had work done to it (other than routine fluid changes). Sounds like its coming up to the slippery slope of the transmission breakdown . Usually this kind of problem is related to the Input Shaft bearing breaking down. Typically, 3rd gear gets hard to get into, and grinds, ect. Eventually you'll experience lots of grinds, up to getting kicked out of gear, even not being able to get into gear at all.

 

check the fluid

 

You could have broken a shift-fork. I don't speak from experience *whistles*