164 auto gearbox need urgent advice

[Anthony Toy <anthonytoy@domain.elided>]

Today when I left for work (a 2 hour commute!) my 91 164 auto wouldn't 
select 2nd gear manually up a hill (it stayed in 3rd). When I reached the 
top I noticed that in drive it wouldn't kick down and changed through the 
gears to early and haphazardly. I stopped the car and noticed that I 
couldn't select reverse except after a few tries. Subsequently I was able 
to drive the car to work and home in manual mode. Occasionally I could 
not get second and sometimes not first (in manual mode). Reverse has 
become very difficult to find, it rquires several tries. On consulting 
the mechanic who works for the people that sold me the car. We have 
concluded that it may be the valve unit for which they have a 
reconditioned change over unit for $400 Australian plus $150 to install 
it. They also have available a manual gearbox change over for $2,000 or 
$3,600 installed which I would have to wait 6 weeks for. My questions are:

1. Does it sound likely to be the valve unit?
2. The car has done 150,000 km, if I change this part, is it likely the 
gearbox may require a complete overhaul soon?
3. How long can I drive the car in this condition before I get stranded?
4. Should I wait and spend the extra money on the manual gearbox and 
enjoy the benefits of performance, economy reliability & fun!
5. How hard would it be for me to fit the manual gearbox myself, an 
experienced backyard mechanic. i.e. do I have to remove the engine? At 
least I could replace those leaking cigarette seals!

Thanks in advance
Anthony Toy
Sydney (Kangaroo Valley) Australia
1991 164L and 1971 1750 GTV

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