I just bought a 69 BSA lightning, checking the fluids but can,t seem to find a fill plug for the transmission.

Well do you see that little ivory colored thing on top of the transmission? That's the dip stick and the fill access.This one found it’s way to Australia a couple of years ago took some wood down there I am told.

what's the deal with importing/exporting bikes. I see it done a lot to aus and japan. Are there tons of fees/taxes, or is it pretty reasonable?

You need a very smart and patient customer at the other side. You need to trust one another and work the system. Brokers are used at both ends they are paid to process the paper work at each port and without them it can get difficult to deal with customs. You have to trust the brokers too. The brokers get both the shipper (you) and the receiver the customer understanding what is needed and what to expect. There are a lot of empty ships leaving the US so the cost isn’t too bad going out of the US.
Now back to the question it is possible for a forty year old bike to be modified with parts from bikes that were make in other years so if your bike does not have a dip stick it is still possible to put oil in so post a picture of yours if you can.

pelican wrote:what's the deal with importing/exporting bikes. I see it done a lot to aus and japan. Are there tons of fees/taxes, or is it pretty reasonable?

I bought a bike in Australia and had it shipped to NZ, can't remember the exact figures but was in the range of $NZ1200 all up, of which only around $400 was shipping. The balance was fees and charges at each port/border. It was a simple process, the freight forwarder did all the paperwork, i just wrote cheques.
Typically you don't pay sales type taxes (VAT, GST etc) in the exporting country (at least in the UK, Aus, NZ that is the case) but you do in the country you import to. So i had to pay 12.5% GST at our border, on the value of the bike including the shipping costs, before customs would release it.