Here's the dilemma.

I have a 1987 300D turbo with 210k miles that has been a great car to own but somewhat of a money pit. After three years of this, however, it is in great shape with new paint and alternator, water pump, vacuum pump, tires, brakes, battery, glow plugs, and many other parts. It's set to go for a long time.

But the transmission leaks. It has since I bought the car. The thing is, it leaked a little 30,000 miles ago. It also intermittently slipped between second and third. I got the fluid changed at the local MB shop and it has been fine ever since. Actually, the shift into third is a little harsh. For a while the shifting was somewhat mushy first thing in the morning, but I found and bypassed the circuit that adds vacuum in cold weather (whose idea was that!) and, after the modulator diaphragm failed, a new modulator made the shifting fine again. Now I am happy with the shifting because it is crisp and timed right.

At this point, however, I have to add fluid every 100 miles because this particular unit shifts poorly if the fluid gets more than a cup low. It's driving me crazy, and the landlord is not happy the 14" diameter puddle on the floor that results from leaving the car parked for more than two days. I have to keep wiping it up, and I cannot go more than a couple hours before stopping to check the ATF!

I can have my mechanic install a good dyno tested rebuilt unit for a total of about $1550. This is a great deal for a good rebuilt transmission. But I have put enough into the car (two major repairs 6 months apart) this year and would much rather put some miles on it and enjoy it for a while. I really cannot afford to throw too much money at a problem that might be fixable for next to nothing. I have a complete set of metric tools and 6 ton jack stands and whatnot, and I can buy or rent a tranny jack for a very reasonable price. I have an able bodied friend indebted to me for other reasons who is willing to come up and help me pull the transmission so that I can replace the seal.

Transmission rebuilders would rather sell me a rebuilt transmission, claiming that the existing tranny will start to leak again if I replace the seal. The Aamco and Cottman guys are shaky at best, but the local MB guy will do the front pump seal (the leaking point) for $650, which is a good deal for the labor involved, but that seems like a poor use of money for a high mileage transmission, since it will cost $750 to do the servo seals too, and that still leaves old seals inside the transmission. I have heard of automatics developing "morning sickness" or slipping in the gears in cold weather due to bad internal seals, and I do not want this to happen to me after lots of expense. I do not currently notice morning sickness on the transmission.

This leaves three options, as far as I can tell:

1) The most affordable thing: to get my friend up here and replace the pump seal and B2 piston and drive the car another couple years if I can, at which point a rebuitl should be more affordable if I need one. Is this something that can be done in a Saturday? Do I have to replace the front pump too? Pump bushing? Anything to be concerned about with the torque convertor? I am figuring $40 for the reseal kit, plus tools, so maybe $100 for this option. What is generally involved in this task?

2) Install a rebuilt myself ($1000) which gives me all new seals and clutches and bands and whatnot, and I don't have to disassemble anything.

3) Pay the independent to install the same rebuilt for the cost of the rebuilt plus his $485.

Does the typical failure mode (if there is one) for these transmissions provide some warning such that I am not risking catastrophe? Can I, a reasonably competent DIYer , complete a reseal in a long day? Is it really likely to leak again from the front pump? When I am not masquerading as a student, I work in the refrigeration industry , where compressor seal failure usually signifies a bad bearing. Someone suggested to me once that I do the front pump bushing as well as the o-ring. Yet another person has suggested replacing the whole pump! Is that overkill?

I would like to take care of this soon because I am losing patience, but I want to strike the right compromise between "doing it right" and staying within my limited budget. Would anyone who has pulled one of these trannies care to comment on the job? Am I approaching this correctly?

Thank you!