Right - I've sorted this without any apparent loss of data.
On the DESTINATION database (NOT the source database):
Remove 138 attribut_id row from catalog_eav_attribute
Remove 138 attribut_id row from eav_entity_attribute
catalog_product_entity_int was an empty table so no action required.
This generated the following error:
Notice: Undefined offset: 18 in /home/porscheshopco/testnewversion/vendor/m
agento/data-migration-tool/src/Migration/Step/Eav/Data.php on line 492
I corrected this by modifying '/vendor/m
agento/data-migration-tool/src/Migration/Step/Eav/Data.php' as per these instructions:
https://github.com/magento/data-migration-tool/commit/ea9cc9f21d3634dd3695fd88f9c869d9535cb6a6
Hope this may be of use to someone else.
Remove 138 attribut_id row from catalog_product_entity_int.
Remove 138 attribut_id row from eav_entity_attribute.
– David Tucker Sep 23 '20 at 11:42