Almost all problems with the Jatco box have either been:
1) Fluid never changed, dirty or wrong fluid used. As it is not expensive to change the fluid, in the UK, this is usually the first thing to try.
2) Faulty solenoid/s. These can be tested fairly easily in the car, can be replaced with box 'in car'.
3) Cracked Revese Piston. (Doesn't affect only reverse) I think you are indicating it is a 1999 model and the early cars up to 2002/2003 frequently suffered this problem. Jatco have modified the part but that doesn't help as you still have to buy the parts ! It is probably the only other fault that can be corrected with 'box in' though needs careful assembly before replacing.
There is a lot of information either in a search (see task bar above) or in the 'How To's. There is a complete description re the revese piston if you do a search, with step by step photo's.
A search should also produce info on the solenoids with testing values given.
Don't know what Km the car has done but the Jatco box is fairly robust to well over 200,000Km with the above exceptions.
By the way the fluid should be changed every 4 years or about 100,000Km but more frequent changes are advisable. Bear in mind only about 60% of the fluid will be changed after a drain & refill. My box had a change at
50, 000Km and will be done again at 100,000
Unless the price allows for a second hand box replacement (late 2003 on) the only alternative is for a transmission specialist to diagnose the problem before you purchase
The solenoids are not particularly expensive to replace but a cracked piston costs around £500-£600, to replace in the UK, by a specialist. The parts are only about £70 ! ! Thing is they usually tut, tut, tut and tell you you need a recon. box but that has probably only had the things mentioned here done.
Profitable business ! ! If you need parts from the UK only buy from:-
www.sussexautos.co.uk Tel:- (44) 1323 848886
Please let me know how you get on
Dave