You can carefully clean the port where you drew the oil for testing.
Then you can connect clean lines to the port and force some oil under pressure back into the transformer.
You can expect that there will be some dirt or contamination that was not able to be cleaned completely.
You can expect this to be carried into the transformer and contaminate the windings.
You can expect the contamination to cause a transformer failure possibly in hours, possibly in days.
You will not sleep easily waiting for the midnight call that the transformer has failed.
How does the cost of a crew for a day compare with the cost of a 100 KVA transformer?
If it is critical, change it now.
If it is not critical, it will probably last years longer if you do nothing.
It it isn't broke, don't broke it.
PS.Don't test the oil again.
Bill
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"Why not the best?"
Jimmy Carter