Problem with 'D' in auto. Have to drive like a manual

Hi guys, problem with my auto 300tdi on Sunday while laning.

My drive gear doesn't work when selected. I have to start in 1st then manually shift to 2nd then 3rd then I can put it in drive. Any ideas? I still have all gears.

If I come
To a stop, I have to go back down to 1 and start going up again. Also if the revs are not high enough it won't shift, it Will just rev.

I changed the ATF and it was very old. Been told to change the filter too as I may have kicked up some crap in the box?
I havnt changed the filter yet as I couldn't get hold of one on the Sunday.
Any ideas?
Cheers

Copied from the Q&As on Ashcroft Transmissions site:

I have a 4sp ZF, when I select "D" the vehicle won't move, when I select "1" the vehicle moves off. I can then select "D" and continue to drive normally. If I stop I have to start in first again. Why?

A sprag clutch has "inverted" and will need replacing. No further damage will occur if you continue to drive but you will need to select "1" every time to start moving. A rebuild is required to correct this.

the oneway clutches (sprag clutch) can sometimes be cured with a clean ,sometimes they are worn enough they do need changing,can be done by a competent diyer

Cheers guys, how much are the sprag clutches? Anyone have a link to one?

I can't seem to find it online.

Cheers